/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.regionserver;

import static org.apache.hadoop.hbase.io.hfile.CacheConfig.CACHE_BLOCKS_ON_WRITE_KEY;
import static org.apache.hadoop.hbase.io.hfile.CacheConfig.CACHE_DATA_ON_READ_KEY;
import static org.apache.hadoop.hbase.io.hfile.CacheConfig.DEFAULT_CACHE_DATA_ON_READ;
import static org.apache.hadoop.hbase.io.hfile.CacheConfig.DEFAULT_CACHE_DATA_ON_WRITE;
import static org.apache.hadoop.hbase.io.hfile.CacheConfig.DEFAULT_EVICT_ON_CLOSE;
import static org.apache.hadoop.hbase.io.hfile.CacheConfig.EVICT_BLOCKS_ON_CLOSE_KEY;
import static org.apache.hadoop.hbase.regionserver.DefaultStoreEngine.DEFAULT_COMPACTION_POLICY_CLASS_KEY;
import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.spy;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.ref.SoftReference;
import java.security.PrivilegedExceptionAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NavigableSet;
import java.util.Optional;
import java.util.TreeSet;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.ConcurrentSkipListSet;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.function.Consumer;
import java.util.function.IntBinaryOperator;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FilterFileSystem;
import org.apache.hadoop.fs.LocalFileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.permission.FsPermission;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellBuilderFactory;
import org.apache.hadoop.hbase.CellBuilderType;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.CellComparatorImpl;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.ExtendedCell;
import org.apache.hadoop.hbase.HBaseClassTestRule;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HBaseTestingUtil;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.MemoryCompactionPolicy;
import org.apache.hadoop.hbase.PrivateCellUtil;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.ColumnFamilyDescriptor;
import org.apache.hadoop.hbase.client.ColumnFamilyDescriptorBuilder;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.RegionInfo;
import org.apache.hadoop.hbase.client.RegionInfoBuilder;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.client.Scan.ReadType;
import org.apache.hadoop.hbase.client.TableDescriptor;
import org.apache.hadoop.hbase.client.TableDescriptorBuilder;
import org.apache.hadoop.hbase.exceptions.IllegalArgumentIOException;
import org.apache.hadoop.hbase.filter.Filter;
import org.apache.hadoop.hbase.filter.FilterBase;
import org.apache.hadoop.hbase.io.compress.Compression;
import org.apache.hadoop.hbase.io.encoding.DataBlockEncoding;
import org.apache.hadoop.hbase.io.hfile.CacheConfig;
import org.apache.hadoop.hbase.io.hfile.HFile;
import org.apache.hadoop.hbase.io.hfile.HFileContext;
import org.apache.hadoop.hbase.io.hfile.HFileContextBuilder;
import org.apache.hadoop.hbase.monitoring.MonitoredTask;
import org.apache.hadoop.hbase.nio.RefCnt;
import org.apache.hadoop.hbase.quotas.RegionSizeStoreImpl;
import org.apache.hadoop.hbase.regionserver.ChunkCreator.ChunkType;
import org.apache.hadoop.hbase.regionserver.MemStoreCompactionStrategy.Action;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionConfiguration;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionContext;
import org.apache.hadoop.hbase.regionserver.compactions.DefaultCompactor;
import org.apache.hadoop.hbase.regionserver.compactions.EverythingPolicy;
import org.apache.hadoop.hbase.regionserver.querymatcher.ScanQueryMatcher;
import org.apache.hadoop.hbase.regionserver.throttle.NoLimitThroughputController;
import org.apache.hadoop.hbase.regionserver.throttle.ThroughputController;
import org.apache.hadoop.hbase.security.User;
import org.apache.hadoop.hbase.testclassification.MediumTests;
import org.apache.hadoop.hbase.testclassification.RegionServerTests;
import org.apache.hadoop.hbase.util.BloomFilterUtil;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.CommonFSUtils;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManagerTestHelper;
import org.apache.hadoop.hbase.util.IncrementingEnvironmentEdge;
import org.apache.hadoop.hbase.util.ManualEnvironmentEdge;
import org.apache.hadoop.hbase.wal.AbstractFSWALProvider;
import org.apache.hadoop.hbase.wal.WALFactory;
import org.apache.hadoop.util.Progressable;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.ClassRule;
import org.junit.Rule;
import org.junit.Test;
import org.junit.experimental.categories.Category;
import org.junit.rules.TestName;
import org.mockito.Mockito;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hbase.thirdparty.com.google.common.collect.Lists;

/**
 * Test class for the HStore
 */
@Category({ RegionServerTests.class, MediumTests.class })
public class TestHStore {

  @ClassRule
  public static final HBaseClassTestRule CLASS_RULE = HBaseClassTestRule.forClass(TestHStore.class);

  private static final Logger LOG = LoggerFactory.getLogger(TestHStore.class);
  @Rule
  public TestName name = new TestName();

  HRegion region;
  HStore store;
  byte[] table = Bytes.toBytes("table");
  byte[] family = Bytes.toBytes("family");

  byte[] row = Bytes.toBytes("row");
  byte[] row2 = Bytes.toBytes("row2");
  byte[] qf1 = Bytes.toBytes("qf1");
  byte[] qf2 = Bytes.toBytes("qf2");
  byte[] qf3 = Bytes.toBytes("qf3");
  byte[] qf4 = Bytes.toBytes("qf4");
  byte[] qf5 = Bytes.toBytes("qf5");
  byte[] qf6 = Bytes.toBytes("qf6");

  NavigableSet<byte[]> qualifiers = new ConcurrentSkipListSet<>(Bytes.BYTES_COMPARATOR);

  List<Cell> expected = new ArrayList<>();
  List<Cell> result = new ArrayList<>();

  long id = EnvironmentEdgeManager.currentTime();
  Get get = new Get(row);

  private static final HBaseTestingUtil TEST_UTIL = new HBaseTestingUtil();
  private static final String DIR = TEST_UTIL.getDataTestDir("TestStore").toString();

  @Before
  public void setUp() throws IOException {
    qualifiers.clear();
    qualifiers.add(qf1);
    qualifiers.add(qf3);
    qualifiers.add(qf5);

    Iterator<byte[]> iter = qualifiers.iterator();
    while (iter.hasNext()) {
      byte[] next = iter.next();
      expected.add(new KeyValue(row, family, next, 1, (byte[]) null));
      get.addColumn(family, next);
    }
  }

  private void init(String methodName) throws IOException {
    init(methodName, TEST_UTIL.getConfiguration());
  }

  private HStore init(String methodName, Configuration conf) throws IOException {
    // some of the tests write 4 versions and then flush
    // (with HBASE-4241, lower versions are collected on flush)
    return init(methodName, conf,
      ColumnFamilyDescriptorBuilder.newBuilder(family).setMaxVersions(4).build());
  }

  private HStore init(String methodName, Configuration conf, ColumnFamilyDescriptor hcd)
    throws IOException {
    return init(methodName, conf, TableDescriptorBuilder.newBuilder(TableName.valueOf(table)), hcd);
  }

  private HStore init(String methodName, Configuration conf, TableDescriptorBuilder builder,
    ColumnFamilyDescriptor hcd) throws IOException {
    return init(methodName, conf, builder, hcd, null);
  }

  private HStore init(String methodName, Configuration conf, TableDescriptorBuilder builder,
    ColumnFamilyDescriptor hcd, MyStoreHook hook) throws IOException {
    return init(methodName, conf, builder, hcd, hook, false);
  }

  private void initHRegion(String methodName, Configuration conf, TableDescriptorBuilder builder,
    ColumnFamilyDescriptor hcd, MyStoreHook hook, boolean switchToPread) throws IOException {
    TableDescriptor htd = builder.setColumnFamily(hcd).build();
    Path basedir = new Path(DIR + methodName);
    Path tableDir = CommonFSUtils.getTableDir(basedir, htd.getTableName());
    final Path logdir = new Path(basedir, AbstractFSWALProvider.getWALDirectoryName(methodName));

    FileSystem fs = FileSystem.get(conf);

    fs.delete(logdir, true);
    ChunkCreator.initialize(MemStoreLAB.CHUNK_SIZE_DEFAULT, false,
      MemStoreLABImpl.CHUNK_SIZE_DEFAULT, 1, 0, null,
      MemStoreLAB.INDEX_CHUNK_SIZE_PERCENTAGE_DEFAULT);
    RegionInfo info = RegionInfoBuilder.newBuilder(htd.getTableName()).build();
    Configuration walConf = new Configuration(conf);
    CommonFSUtils.setRootDir(walConf, basedir);
    WALFactory wals = new WALFactory(walConf, methodName);
    region = new HRegion(new HRegionFileSystem(conf, fs, tableDir, info), wals.getWAL(info), conf,
      htd, null);
    region.regionServicesForStores = Mockito.spy(region.regionServicesForStores);
    ThreadPoolExecutor pool = (ThreadPoolExecutor) Executors.newFixedThreadPool(1);
    Mockito.when(region.regionServicesForStores.getInMemoryCompactionPool()).thenReturn(pool);
  }

  private HStore init(String methodName, Configuration conf, TableDescriptorBuilder builder,
    ColumnFamilyDescriptor hcd, MyStoreHook hook, boolean switchToPread) throws IOException {
    initHRegion(methodName, conf, builder, hcd, hook, switchToPread);
    if (hook == null) {
      store = new HStore(region, hcd, conf, false);
    } else {
      store = new MyStore(region, hcd, conf, hook, switchToPread);
    }
    region.stores.put(store.getColumnFamilyDescriptor().getName(), store);
    return store;
  }

  /**
   * Test we do not lose data if we fail a flush and then close. Part of HBase-10466
   */
  @Test
  public void testFlushSizeSizing() throws Exception {
    LOG.info("Setting up a faulty file system that cannot write in " + this.name.getMethodName());
    final Configuration conf = HBaseConfiguration.create(TEST_UTIL.getConfiguration());
    // Only retry once.
    conf.setInt("hbase.hstore.flush.retries.number", 1);
    User user = User.createUserForTesting(conf, this.name.getMethodName(), new String[] { "foo" });
    // Inject our faulty LocalFileSystem
    conf.setClass("fs.file.impl", FaultyFileSystem.class, FileSystem.class);
    user.runAs(new PrivilegedExceptionAction<Object>() {
      @Override
      public Object run() throws Exception {
        // Make sure it worked (above is sensitive to caching details in hadoop core)
        FileSystem fs = FileSystem.get(conf);
        assertEquals(FaultyFileSystem.class, fs.getClass());
        FaultyFileSystem ffs = (FaultyFileSystem) fs;

        // Initialize region
        init(name.getMethodName(), conf);

        MemStoreSize mss = store.memstore.getFlushableSize();
        assertEquals(0, mss.getDataSize());
        LOG.info("Adding some data");
        MemStoreSizing kvSize = new NonThreadSafeMemStoreSizing();
        store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), kvSize);
        // add the heap size of active (mutable) segment
        kvSize.incMemStoreSize(0, MutableSegment.DEEP_OVERHEAD, 0, 0);
        mss = store.memstore.getFlushableSize();
        assertEquals(kvSize.getMemStoreSize(), mss);
        // Flush. Bug #1 from HBASE-10466. Make sure size calculation on failed flush is right.
        try {
          LOG.info("Flushing");
          flushStore(store, id++);
          fail("Didn't bubble up IOE!");
        } catch (IOException ioe) {
          assertTrue(ioe.getMessage().contains("Fault injected"));
        }
        // due to snapshot, change mutable to immutable segment
        kvSize.incMemStoreSize(0,
          CSLMImmutableSegment.DEEP_OVERHEAD_CSLM - MutableSegment.DEEP_OVERHEAD, 0, 0);
        mss = store.memstore.getFlushableSize();
        assertEquals(kvSize.getMemStoreSize(), mss);
        MemStoreSizing kvSize2 = new NonThreadSafeMemStoreSizing();
        store.add(new KeyValue(row, family, qf2, 2, (byte[]) null), kvSize2);
        kvSize2.incMemStoreSize(0, MutableSegment.DEEP_OVERHEAD, 0, 0);
        // Even though we add a new kv, we expect the flushable size to be 'same' since we have
        // not yet cleared the snapshot -- the above flush failed.
        assertEquals(kvSize.getMemStoreSize(), mss);
        ffs.fault.set(false);
        flushStore(store, id++);
        mss = store.memstore.getFlushableSize();
        // Size should be the foreground kv size.
        assertEquals(kvSize2.getMemStoreSize(), mss);
        flushStore(store, id++);
        mss = store.memstore.getFlushableSize();
        assertEquals(0, mss.getDataSize());
        assertEquals(MutableSegment.DEEP_OVERHEAD, mss.getHeapSize());
        return null;
      }
    });
  }

  @Test
  public void testStoreBloomFilterMetricsWithBloomRowCol() throws IOException {
    int numStoreFiles = 5;
    writeAndRead(BloomType.ROWCOL, numStoreFiles);

    assertEquals(0, store.getBloomFilterEligibleRequestsCount());
    // hard to know exactly the numbers here, we are just trying to
    // prove that they are incrementing
    assertTrue(store.getBloomFilterRequestsCount() >= numStoreFiles);
    assertTrue(store.getBloomFilterNegativeResultsCount() > 0);
  }

  @Test
  public void testStoreBloomFilterMetricsWithBloomRow() throws IOException {
    int numStoreFiles = 5;
    writeAndRead(BloomType.ROWCOL, numStoreFiles);

    assertEquals(0, store.getBloomFilterEligibleRequestsCount());
    // hard to know exactly the numbers here, we are just trying to
    // prove that they are incrementing
    assertTrue(store.getBloomFilterRequestsCount() >= numStoreFiles);
    assertTrue(store.getBloomFilterNegativeResultsCount() > 0);
  }

  @Test
  public void testStoreBloomFilterMetricsWithBloomRowPrefix() throws IOException {
    int numStoreFiles = 5;
    writeAndRead(BloomType.ROWPREFIX_FIXED_LENGTH, numStoreFiles);

    assertEquals(0, store.getBloomFilterEligibleRequestsCount());
    // hard to know exactly the numbers here, we are just trying to
    // prove that they are incrementing
    assertTrue(store.getBloomFilterRequestsCount() >= numStoreFiles);
  }

  @Test
  public void testStoreBloomFilterMetricsWithBloomNone() throws IOException {
    int numStoreFiles = 5;
    writeAndRead(BloomType.NONE, numStoreFiles);

    assertEquals(0, store.getBloomFilterRequestsCount());
    assertEquals(0, store.getBloomFilterNegativeResultsCount());

    // hard to know exactly the numbers here, we are just trying to
    // prove that they are incrementing
    assertTrue(store.getBloomFilterEligibleRequestsCount() >= numStoreFiles);
  }

  private void writeAndRead(BloomType bloomType, int numStoreFiles) throws IOException {
    Configuration conf = HBaseConfiguration.create();
    FileSystem fs = FileSystem.get(conf);

    ColumnFamilyDescriptor hcd = ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setCompressionType(Compression.Algorithm.GZ).setBloomFilterType(bloomType)
      .setConfiguration(BloomFilterUtil.PREFIX_LENGTH_KEY, "3").build();
    init(name.getMethodName(), conf, hcd);

    for (int i = 1; i <= numStoreFiles; i++) {
      byte[] row = Bytes.toBytes("row" + i);
      LOG.info("Adding some data for the store file #" + i);
      long timeStamp = EnvironmentEdgeManager.currentTime();
      this.store.add(new KeyValue(row, family, qf1, timeStamp, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf2, timeStamp, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf3, timeStamp, (byte[]) null), null);
      flush(i);
    }

    // Verify the total number of store files
    assertEquals(numStoreFiles, this.store.getStorefiles().size());

    TreeSet<byte[]> columns = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    columns.add(qf1);

    for (int i = 1; i <= numStoreFiles; i++) {
      KeyValueScanner scanner =
        store.getScanner(new Scan(new Get(Bytes.toBytes("row" + i))), columns, 0);
      scanner.peek();
    }
  }

  /**
   * Verify that compression and data block encoding are respected by the createWriter method, used
   * on store flush.
   */
  @Test
  public void testCreateWriter() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    FileSystem fs = FileSystem.get(conf);

    ColumnFamilyDescriptor hcd =
      ColumnFamilyDescriptorBuilder.newBuilder(family).setCompressionType(Compression.Algorithm.GZ)
        .setDataBlockEncoding(DataBlockEncoding.DIFF).build();
    init(name.getMethodName(), conf, hcd);

    // Test createWriter
    StoreFileWriter writer = store.getStoreEngine()
      .createWriter(CreateStoreFileWriterParams.create().maxKeyCount(4)
        .compression(hcd.getCompressionType()).isCompaction(false).includeMVCCReadpoint(true)
        .includesTag(false).shouldDropBehind(false));
    Path path = writer.getPath();
    writer.append(new KeyValue(row, family, qf1, Bytes.toBytes(1)));
    writer.append(new KeyValue(row, family, qf2, Bytes.toBytes(2)));
    writer.append(new KeyValue(row2, family, qf1, Bytes.toBytes(3)));
    writer.append(new KeyValue(row2, family, qf2, Bytes.toBytes(4)));
    writer.close();

    // Verify that compression and encoding settings are respected
    HFile.Reader reader = HFile.createReader(fs, path, new CacheConfig(conf), true, conf);
    assertEquals(hcd.getCompressionType(), reader.getTrailer().getCompressionCodec());
    assertEquals(hcd.getDataBlockEncoding(), reader.getDataBlockEncoding());
    reader.close();
  }

  @Test
  public void testDeleteExpiredStoreFiles() throws Exception {
    testDeleteExpiredStoreFiles(0);
    testDeleteExpiredStoreFiles(1);
  }

  /**
   * @param minVersions the MIN_VERSIONS for the column family
   */
  public void testDeleteExpiredStoreFiles(int minVersions) throws Exception {
    int storeFileNum = 4;
    int ttl = 4;
    IncrementingEnvironmentEdge edge = new IncrementingEnvironmentEdge();
    EnvironmentEdgeManagerTestHelper.injectEdge(edge);

    Configuration conf = HBaseConfiguration.create();
    // Enable the expired store file deletion
    conf.setBoolean("hbase.store.delete.expired.storefile", true);
    // Set the compaction threshold higher to avoid normal compactions.
    conf.setInt(CompactionConfiguration.HBASE_HSTORE_COMPACTION_MIN_KEY, 5);

    init(name.getMethodName() + "-" + minVersions, conf, ColumnFamilyDescriptorBuilder
      .newBuilder(family).setMinVersions(minVersions).setTimeToLive(ttl).build());

    long storeTtl = this.store.getScanInfo().getTtl();
    long sleepTime = storeTtl / storeFileNum;
    long timeStamp;
    // There are 4 store files and the max time stamp difference among these
    // store files will be (this.store.ttl / storeFileNum)
    for (int i = 1; i <= storeFileNum; i++) {
      LOG.info("Adding some data for the store file #" + i);
      timeStamp = EnvironmentEdgeManager.currentTime();
      this.store.add(new KeyValue(row, family, qf1, timeStamp, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf2, timeStamp, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf3, timeStamp, (byte[]) null), null);
      flush(i);
      edge.incrementTime(sleepTime);
    }

    // Verify the total number of store files
    assertEquals(storeFileNum, this.store.getStorefiles().size());

    // Each call will find one expired store file and delete it before compaction happens.
    // There will be no compaction due to threshold above. Last file will not be replaced.
    for (int i = 1; i <= storeFileNum - 1; i++) {
      // verify the expired store file.
      assertFalse(this.store.requestCompaction().isPresent());
      Collection<HStoreFile> sfs = this.store.getStorefiles();
      // Ensure i files are gone.
      if (minVersions == 0) {
        assertEquals(storeFileNum - i, sfs.size());
        // Ensure only non-expired files remain.
        for (HStoreFile sf : sfs) {
          assertTrue(sf.getReader().getMaxTimestamp() >= (edge.currentTime() - storeTtl));
        }
      } else {
        assertEquals(storeFileNum, sfs.size());
      }
      // Let the next store file expired.
      edge.incrementTime(sleepTime);
    }
    assertFalse(this.store.requestCompaction().isPresent());

    Collection<HStoreFile> sfs = this.store.getStorefiles();
    // Assert the last expired file is not removed.
    if (minVersions == 0) {
      assertEquals(1, sfs.size());
    }
    long ts = sfs.iterator().next().getReader().getMaxTimestamp();
    assertTrue(ts < (edge.currentTime() - storeTtl));

    for (HStoreFile sf : sfs) {
      sf.closeStoreFile(true);
    }
  }

  @Test
  public void testLowestModificationTime() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    FileSystem fs = FileSystem.get(conf);
    // Initialize region
    init(name.getMethodName(), conf);

    int storeFileNum = 4;
    for (int i = 1; i <= storeFileNum; i++) {
      LOG.info("Adding some data for the store file #" + i);
      this.store.add(new KeyValue(row, family, qf1, i, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf2, i, (byte[]) null), null);
      this.store.add(new KeyValue(row, family, qf3, i, (byte[]) null), null);
      flush(i);
    }
    // after flush; check the lowest time stamp
    long lowestTimeStampFromManager = StoreUtils.getLowestTimestamp(store.getStorefiles());
    long lowestTimeStampFromFS = getLowestTimeStampFromFS(fs, store.getStorefiles());
    assertEquals(lowestTimeStampFromManager, lowestTimeStampFromFS);

    // after compact; check the lowest time stamp
    store.compact(store.requestCompaction().get(), NoLimitThroughputController.INSTANCE, null);
    lowestTimeStampFromManager = StoreUtils.getLowestTimestamp(store.getStorefiles());
    lowestTimeStampFromFS = getLowestTimeStampFromFS(fs, store.getStorefiles());
    assertEquals(lowestTimeStampFromManager, lowestTimeStampFromFS);
  }

  private static long getLowestTimeStampFromFS(FileSystem fs,
    final Collection<HStoreFile> candidates) throws IOException {
    long minTs = Long.MAX_VALUE;
    if (candidates.isEmpty()) {
      return minTs;
    }
    Path[] p = new Path[candidates.size()];
    int i = 0;
    for (HStoreFile sf : candidates) {
      p[i] = sf.getPath();
      ++i;
    }

    FileStatus[] stats = fs.listStatus(p);
    if (stats == null || stats.length == 0) {
      return minTs;
    }
    for (FileStatus s : stats) {
      minTs = Math.min(minTs, s.getModificationTime());
    }
    return minTs;
  }

  //////////////////////////////////////////////////////////////////////////////
  // Get tests
  //////////////////////////////////////////////////////////////////////////////

  private static final int BLOCKSIZE_SMALL = 8192;

  /**
   * Test for hbase-1686.
   */
  @Test
  public void testEmptyStoreFile() throws IOException {
    init(this.name.getMethodName());
    // Write a store file.
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf2, 1, (byte[]) null), null);
    flush(1);
    // Now put in place an empty store file. Its a little tricky. Have to
    // do manually with hacked in sequence id.
    HStoreFile f = this.store.getStorefiles().iterator().next();
    Path storedir = f.getPath().getParent();
    long seqid = f.getMaxSequenceId();
    Configuration c = HBaseConfiguration.create();
    FileSystem fs = FileSystem.get(c);
    HFileContext meta = new HFileContextBuilder().withBlockSize(BLOCKSIZE_SMALL).build();
    StoreFileWriter w = new StoreFileWriter.Builder(c, new CacheConfig(c), fs)
      .withOutputDir(storedir).withFileContext(meta).build();
    w.appendMetadata(seqid + 1, false);
    w.close();
    this.store.close();
    // Reopen it... should pick up two files
    this.store =
      new HStore(this.store.getHRegion(), this.store.getColumnFamilyDescriptor(), c, false);
    assertEquals(2, this.store.getStorefilesCount());

    result = HBaseTestingUtil.getFromStoreFile(store, get.getRow(), qualifiers);
    assertEquals(1, result.size());
  }

  /**
   * Getting data from memstore only
   */
  @Test
  public void testGet_FromMemStoreOnly() throws IOException {
    init(this.name.getMethodName());

    // Put data in memstore
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf2, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf3, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf4, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf5, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf6, 1, (byte[]) null), null);

    // Get
    result = HBaseTestingUtil.getFromStoreFile(store, get.getRow(), qualifiers);

    // Compare
    assertCheck();
  }

  @Test
  public void testTimeRangeIfSomeCellsAreDroppedInFlush() throws IOException {
    testTimeRangeIfSomeCellsAreDroppedInFlush(1);
    testTimeRangeIfSomeCellsAreDroppedInFlush(3);
    testTimeRangeIfSomeCellsAreDroppedInFlush(5);
  }

  private void testTimeRangeIfSomeCellsAreDroppedInFlush(int maxVersion) throws IOException {
    init(this.name.getMethodName(), TEST_UTIL.getConfiguration(),
      ColumnFamilyDescriptorBuilder.newBuilder(family).setMaxVersions(maxVersion).build());
    long currentTs = 100;
    long minTs = currentTs;
    // the extra cell won't be flushed to disk,
    // so the min of timerange will be different between memStore and hfile.
    for (int i = 0; i != (maxVersion + 1); ++i) {
      this.store.add(new KeyValue(row, family, qf1, ++currentTs, (byte[]) null), null);
      if (i == 1) {
        minTs = currentTs;
      }
    }
    flushStore(store, id++);

    Collection<HStoreFile> files = store.getStorefiles();
    assertEquals(1, files.size());
    HStoreFile f = files.iterator().next();
    f.initReader();
    StoreFileReader reader = f.getReader();
    assertEquals(minTs, reader.timeRange.getMin());
    assertEquals(currentTs, reader.timeRange.getMax());
  }

  /**
   * Getting data from files only
   */
  @Test
  public void testGet_FromFilesOnly() throws IOException {
    init(this.name.getMethodName());

    // Put data in memstore
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf2, 1, (byte[]) null), null);
    // flush
    flush(1);

    // Add more data
    this.store.add(new KeyValue(row, family, qf3, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf4, 1, (byte[]) null), null);
    // flush
    flush(2);

    // Add more data
    this.store.add(new KeyValue(row, family, qf5, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf6, 1, (byte[]) null), null);
    // flush
    flush(3);

    // Get
    result = HBaseTestingUtil.getFromStoreFile(store, get.getRow(), qualifiers);
    // this.store.get(get, qualifiers, result);

    // Need to sort the result since multiple files
    Collections.sort(result, CellComparatorImpl.COMPARATOR);

    // Compare
    assertCheck();
  }

  /**
   * Getting data from memstore and files
   */
  @Test
  public void testGet_FromMemStoreAndFiles() throws IOException {
    init(this.name.getMethodName());

    // Put data in memstore
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf2, 1, (byte[]) null), null);
    // flush
    flush(1);

    // Add more data
    this.store.add(new KeyValue(row, family, qf3, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf4, 1, (byte[]) null), null);
    // flush
    flush(2);

    // Add more data
    this.store.add(new KeyValue(row, family, qf5, 1, (byte[]) null), null);
    this.store.add(new KeyValue(row, family, qf6, 1, (byte[]) null), null);

    // Get
    result = HBaseTestingUtil.getFromStoreFile(store, get.getRow(), qualifiers);

    // Need to sort the result since multiple files
    Collections.sort(result, CellComparatorImpl.COMPARATOR);

    // Compare
    assertCheck();
  }

  private void flush(int storeFilessize) throws IOException {
    flushStore(store, id++);
    assertEquals(storeFilessize, this.store.getStorefiles().size());
    assertEquals(0, ((AbstractMemStore) this.store.memstore).getActive().getCellsCount());
  }

  private void assertCheck() {
    assertEquals(expected.size(), result.size());
    for (int i = 0; i < expected.size(); i++) {
      assertEquals(expected.get(i), result.get(i));
    }
  }

  @After
  public void tearDown() throws Exception {
    EnvironmentEdgeManagerTestHelper.reset();
    if (store != null) {
      try {
        store.close();
      } catch (IOException e) {
      }
      store = null;
    }
    if (region != null) {
      region.close();
      region = null;
    }
  }

  @AfterClass
  public static void tearDownAfterClass() throws IOException {
    TEST_UTIL.cleanupTestDir();
  }

  @Test
  public void testHandleErrorsInFlush() throws Exception {
    LOG.info("Setting up a faulty file system that cannot write");

    final Configuration conf = HBaseConfiguration.create(TEST_UTIL.getConfiguration());
    User user = User.createUserForTesting(conf, "testhandleerrorsinflush", new String[] { "foo" });
    // Inject our faulty LocalFileSystem
    conf.setClass("fs.file.impl", FaultyFileSystem.class, FileSystem.class);
    user.runAs(new PrivilegedExceptionAction<Object>() {
      @Override
      public Object run() throws Exception {
        // Make sure it worked (above is sensitive to caching details in hadoop core)
        FileSystem fs = FileSystem.get(conf);
        assertEquals(FaultyFileSystem.class, fs.getClass());

        // Initialize region
        init(name.getMethodName(), conf);

        LOG.info("Adding some data");
        store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
        store.add(new KeyValue(row, family, qf2, 1, (byte[]) null), null);
        store.add(new KeyValue(row, family, qf3, 1, (byte[]) null), null);

        LOG.info("Before flush, we should have no files");

        Collection<StoreFileInfo> files =
          store.getRegionFileSystem().getStoreFiles(store.getColumnFamilyName());
        assertEquals(0, files != null ? files.size() : 0);

        // flush
        try {
          LOG.info("Flushing");
          flush(1);
          fail("Didn't bubble up IOE!");
        } catch (IOException ioe) {
          assertTrue(ioe.getMessage().contains("Fault injected"));
        }

        LOG.info("After failed flush, we should still have no files!");
        files = store.getRegionFileSystem().getStoreFiles(store.getColumnFamilyName());
        assertEquals(0, files != null ? files.size() : 0);
        store.getHRegion().getWAL().close();
        return null;
      }
    });
    FileSystem.closeAllForUGI(user.getUGI());
  }

  /**
   * Faulty file system that will fail if you write past its fault position the FIRST TIME only;
   * thereafter it will succeed. Used by {@link TestHRegion} too.
   */
  static class FaultyFileSystem extends FilterFileSystem {
    List<SoftReference<FaultyOutputStream>> outStreams = new ArrayList<>();
    private long faultPos = 200;
    AtomicBoolean fault = new AtomicBoolean(true);

    public FaultyFileSystem() {
      super(new LocalFileSystem());
      LOG.info("Creating faulty!");
    }

    @Override
    public FSDataOutputStream create(Path p) throws IOException {
      return new FaultyOutputStream(super.create(p), faultPos, fault);
    }

    @Override
    public FSDataOutputStream create(Path f, FsPermission permission, boolean overwrite,
      int bufferSize, short replication, long blockSize, Progressable progress) throws IOException {
      return new FaultyOutputStream(
        super.create(f, permission, overwrite, bufferSize, replication, blockSize, progress),
        faultPos, fault);
    }

    @Override
    public FSDataOutputStream createNonRecursive(Path f, boolean overwrite, int bufferSize,
      short replication, long blockSize, Progressable progress) throws IOException {
      // Fake it. Call create instead. The default implementation throws an IOE
      // that this is not supported.
      return create(f, overwrite, bufferSize, replication, blockSize, progress);
    }
  }

  static class FaultyOutputStream extends FSDataOutputStream {
    volatile long faultPos = Long.MAX_VALUE;
    private final AtomicBoolean fault;

    public FaultyOutputStream(FSDataOutputStream out, long faultPos, final AtomicBoolean fault)
      throws IOException {
      super(out, null);
      this.faultPos = faultPos;
      this.fault = fault;
    }

    @Override
    public synchronized void write(byte[] buf, int offset, int length) throws IOException {
      LOG.info("faulty stream write at pos " + getPos());
      injectFault();
      super.write(buf, offset, length);
    }

    private void injectFault() throws IOException {
      if (this.fault.get() && getPos() >= faultPos) {
        throw new IOException("Fault injected");
      }
    }
  }

  private static StoreFlushContext flushStore(HStore store, long id) throws IOException {
    StoreFlushContext storeFlushCtx = store.createFlushContext(id, FlushLifeCycleTracker.DUMMY);
    storeFlushCtx.prepare();
    storeFlushCtx.flushCache(Mockito.mock(MonitoredTask.class));
    storeFlushCtx.commit(Mockito.mock(MonitoredTask.class));
    return storeFlushCtx;
  }

  /**
   * Generate a list of KeyValues for testing based on given parameters
   * @return the rows key-value list
   */
  private List<Cell> getKeyValueSet(long[] timestamps, int numRows, byte[] qualifier,
    byte[] family) {
    List<Cell> kvList = new ArrayList<>();
    for (int i = 1; i <= numRows; i++) {
      byte[] b = Bytes.toBytes(i);
      for (long timestamp : timestamps) {
        kvList.add(new KeyValue(b, family, qualifier, timestamp, b));
      }
    }
    return kvList;
  }

  /**
   * Test to ensure correctness when using Stores with multiple timestamps
   */
  @Test
  public void testMultipleTimestamps() throws IOException {
    int numRows = 1;
    long[] timestamps1 = new long[] { 1, 5, 10, 20 };
    long[] timestamps2 = new long[] { 30, 80 };

    init(this.name.getMethodName());

    List<Cell> kvList1 = getKeyValueSet(timestamps1, numRows, qf1, family);
    for (Cell kv : kvList1) {
      this.store.add(kv, null);
    }

    flushStore(store, id++);

    List<Cell> kvList2 = getKeyValueSet(timestamps2, numRows, qf1, family);
    for (Cell kv : kvList2) {
      this.store.add(kv, null);
    }

    List<Cell> result;
    Get get = new Get(Bytes.toBytes(1));
    get.addColumn(family, qf1);

    get.setTimeRange(0, 15);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() > 0);

    get.setTimeRange(40, 90);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() > 0);

    get.setTimeRange(10, 45);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() > 0);

    get.setTimeRange(80, 145);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() > 0);

    get.setTimeRange(1, 2);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() > 0);

    get.setTimeRange(90, 200);
    result = HBaseTestingUtil.getFromStoreFile(store, get);
    assertTrue(result.size() == 0);
  }

  /**
   * Test for HBASE-3492 - Test split on empty colfam (no store files).
   * @throws IOException When the IO operations fail.
   */
  @Test
  public void testSplitWithEmptyColFam() throws IOException {
    init(this.name.getMethodName());
    assertFalse(store.getSplitPoint().isPresent());
  }

  @Test
  public void testStoreUsesConfigurationFromHcdAndHtd() throws Exception {
    final String CONFIG_KEY = "hbase.regionserver.thread.compaction.throttle";
    long anyValue = 10;

    // We'll check that it uses correct config and propagates it appropriately by going thru
    // the simplest "real" path I can find - "throttleCompaction", which just checks whether
    // a number we pass in is higher than some config value, inside compactionPolicy.
    Configuration conf = HBaseConfiguration.create();
    conf.setLong(CONFIG_KEY, anyValue);
    init(name.getMethodName() + "-xml", conf);
    assertTrue(store.throttleCompaction(anyValue + 1));
    assertFalse(store.throttleCompaction(anyValue));

    // HTD overrides XML.
    --anyValue;
    init(
      name.getMethodName() + "-htd", conf, TableDescriptorBuilder
        .newBuilder(TableName.valueOf(table)).setValue(CONFIG_KEY, Long.toString(anyValue)),
      ColumnFamilyDescriptorBuilder.of(family));
    assertTrue(store.throttleCompaction(anyValue + 1));
    assertFalse(store.throttleCompaction(anyValue));

    // HCD overrides them both.
    --anyValue;
    init(name.getMethodName() + "-hcd", conf,
      TableDescriptorBuilder.newBuilder(TableName.valueOf(table)).setValue(CONFIG_KEY,
        Long.toString(anyValue)),
      ColumnFamilyDescriptorBuilder.newBuilder(family).setValue(CONFIG_KEY, Long.toString(anyValue))
        .build());
    assertTrue(store.throttleCompaction(anyValue + 1));
    assertFalse(store.throttleCompaction(anyValue));
  }

  public static class DummyStoreEngine extends DefaultStoreEngine {
    public static DefaultCompactor lastCreatedCompactor = null;

    @Override
    protected void createComponents(Configuration conf, HStore store, CellComparator comparator)
      throws IOException {
      super.createComponents(conf, store, comparator);
      lastCreatedCompactor = this.compactor;
    }
  }

  @Test
  public void testStoreUsesSearchEngineOverride() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    conf.set(StoreEngine.STORE_ENGINE_CLASS_KEY, DummyStoreEngine.class.getName());
    init(this.name.getMethodName(), conf);
    assertEquals(DummyStoreEngine.lastCreatedCompactor, this.store.storeEngine.getCompactor());
  }

  private void addStoreFile() throws IOException {
    HStoreFile f = this.store.getStorefiles().iterator().next();
    Path storedir = f.getPath().getParent();
    long seqid = this.store.getMaxSequenceId().orElse(0L);
    Configuration c = TEST_UTIL.getConfiguration();
    FileSystem fs = FileSystem.get(c);
    HFileContext fileContext = new HFileContextBuilder().withBlockSize(BLOCKSIZE_SMALL).build();
    StoreFileWriter w = new StoreFileWriter.Builder(c, new CacheConfig(c), fs)
      .withOutputDir(storedir).withFileContext(fileContext).build();
    w.appendMetadata(seqid + 1, false);
    w.close();
    LOG.info("Added store file:" + w.getPath());
  }

  private void archiveStoreFile(int index) throws IOException {
    Collection<HStoreFile> files = this.store.getStorefiles();
    HStoreFile sf = null;
    Iterator<HStoreFile> it = files.iterator();
    for (int i = 0; i <= index; i++) {
      sf = it.next();
    }
    store.getRegionFileSystem().removeStoreFiles(store.getColumnFamilyName(),
      Lists.newArrayList(sf));
  }

  private void closeCompactedFile(int index) throws IOException {
    Collection<HStoreFile> files =
      this.store.getStoreEngine().getStoreFileManager().getCompactedfiles();
    if (files.size() > 0) {
      HStoreFile sf = null;
      Iterator<HStoreFile> it = files.iterator();
      for (int i = 0; i <= index; i++) {
        sf = it.next();
      }
      sf.closeStoreFile(true);
      store.getStoreEngine().getStoreFileManager()
        .removeCompactedFiles(Collections.singletonList(sf));
    }
  }

  @Test
  public void testRefreshStoreFiles() throws Exception {
    init(name.getMethodName());

    assertEquals(0, this.store.getStorefilesCount());

    // Test refreshing store files when no store files are there
    store.refreshStoreFiles();
    assertEquals(0, this.store.getStorefilesCount());

    // add some data, flush
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    flush(1);
    assertEquals(1, this.store.getStorefilesCount());

    // add one more file
    addStoreFile();

    assertEquals(1, this.store.getStorefilesCount());
    store.refreshStoreFiles();
    assertEquals(2, this.store.getStorefilesCount());

    // add three more files
    addStoreFile();
    addStoreFile();
    addStoreFile();

    assertEquals(2, this.store.getStorefilesCount());
    store.refreshStoreFiles();
    assertEquals(5, this.store.getStorefilesCount());

    closeCompactedFile(0);
    archiveStoreFile(0);

    assertEquals(5, this.store.getStorefilesCount());
    store.refreshStoreFiles();
    assertEquals(4, this.store.getStorefilesCount());

    archiveStoreFile(0);
    archiveStoreFile(1);
    archiveStoreFile(2);

    assertEquals(4, this.store.getStorefilesCount());
    store.refreshStoreFiles();
    assertEquals(1, this.store.getStorefilesCount());

    archiveStoreFile(0);
    store.refreshStoreFiles();
    assertEquals(0, this.store.getStorefilesCount());
  }

  @Test
  public void testRefreshStoreFilesNotChanged() throws IOException {
    init(name.getMethodName());

    assertEquals(0, this.store.getStorefilesCount());

    // add some data, flush
    this.store.add(new KeyValue(row, family, qf1, 1, (byte[]) null), null);
    flush(1);
    // add one more file
    addStoreFile();

    StoreEngine<?, ?, ?, ?> spiedStoreEngine = spy(store.getStoreEngine());

    // call first time after files changed
    spiedStoreEngine.refreshStoreFiles();
    assertEquals(2, this.store.getStorefilesCount());
    verify(spiedStoreEngine, times(1)).replaceStoreFiles(any(), any(), any(), any());

    // call second time
    spiedStoreEngine.refreshStoreFiles();

    // ensure that replaceStoreFiles is not called, i.e, the times does not change, if files are not
    // refreshed,
    verify(spiedStoreEngine, times(1)).replaceStoreFiles(any(), any(), any(), any());
  }

  @Test
  public void testScanWithCompactionAfterFlush() throws Exception {
    TEST_UTIL.getConfiguration().set(DEFAULT_COMPACTION_POLICY_CLASS_KEY,
      EverythingPolicy.class.getName());
    init(name.getMethodName());

    assertEquals(0, this.store.getStorefilesCount());

    KeyValue kv = new KeyValue(row, family, qf1, 1, (byte[]) null);
    // add some data, flush
    this.store.add(kv, null);
    flush(1);
    kv = new KeyValue(row, family, qf2, 1, (byte[]) null);
    // add some data, flush
    this.store.add(kv, null);
    flush(2);
    kv = new KeyValue(row, family, qf3, 1, (byte[]) null);
    // add some data, flush
    this.store.add(kv, null);
    flush(3);

    ExecutorService service = Executors.newFixedThreadPool(2);

    Scan scan = new Scan(new Get(row));
    Future<KeyValueScanner> scanFuture = service.submit(() -> {
      try {
        LOG.info(">>>> creating scanner");
        return this.store.createScanner(scan,
          new ScanInfo(HBaseConfiguration.create(),
            ColumnFamilyDescriptorBuilder.newBuilder(family).setMaxVersions(4).build(),
            Long.MAX_VALUE, 0, CellComparator.getInstance()),
          scan.getFamilyMap().get(store.getColumnFamilyDescriptor().getName()), 0);
      } catch (IOException e) {
        e.printStackTrace();
        return null;
      }
    });
    Future compactFuture = service.submit(() -> {
      try {
        LOG.info(">>>>>> starting compaction");
        Optional<CompactionContext> opCompaction = this.store.requestCompaction();
        assertTrue(opCompaction.isPresent());
        store.compact(opCompaction.get(), new NoLimitThroughputController(), User.getCurrent());
        LOG.info(">>>>>> Compaction is finished");
        this.store.closeAndArchiveCompactedFiles();
        LOG.info(">>>>>> Compacted files deleted");
      } catch (IOException e) {
        e.printStackTrace();
      }
    });

    KeyValueScanner kvs = scanFuture.get();
    compactFuture.get();
    ((StoreScanner) kvs).currentScanners.forEach(s -> {
      if (s instanceof StoreFileScanner) {
        assertEquals(1, ((StoreFileScanner) s).getReader().getRefCount());
      }
    });
    kvs.seek(kv);
    service.shutdownNow();
  }

  private long countMemStoreScanner(StoreScanner scanner) {
    if (scanner.currentScanners == null) {
      return 0;
    }
    return scanner.currentScanners.stream().filter(s -> !s.isFileScanner()).count();
  }

  @Test
  public void testNumberOfMemStoreScannersAfterFlush() throws IOException {
    long seqId = 100;
    long timestamp = EnvironmentEdgeManager.currentTime();
    Cell cell0 = CellBuilderFactory.create(CellBuilderType.DEEP_COPY).setRow(row).setFamily(family)
      .setQualifier(qf1).setTimestamp(timestamp).setType(Cell.Type.Put).setValue(qf1).build();
    PrivateCellUtil.setSequenceId(cell0, seqId);
    testNumberOfMemStoreScannersAfterFlush(Arrays.asList(cell0), Collections.emptyList());

    Cell cell1 = CellBuilderFactory.create(CellBuilderType.DEEP_COPY).setRow(row).setFamily(family)
      .setQualifier(qf2).setTimestamp(timestamp).setType(Cell.Type.Put).setValue(qf1).build();
    PrivateCellUtil.setSequenceId(cell1, seqId);
    testNumberOfMemStoreScannersAfterFlush(Arrays.asList(cell0), Arrays.asList(cell1));

    seqId = 101;
    timestamp = EnvironmentEdgeManager.currentTime();
    Cell cell2 = CellBuilderFactory.create(CellBuilderType.DEEP_COPY).setRow(row2).setFamily(family)
      .setQualifier(qf2).setTimestamp(timestamp).setType(Cell.Type.Put).setValue(qf1).build();
    PrivateCellUtil.setSequenceId(cell2, seqId);
    testNumberOfMemStoreScannersAfterFlush(Arrays.asList(cell0), Arrays.asList(cell1, cell2));
  }

  private void testNumberOfMemStoreScannersAfterFlush(List<Cell> inputCellsBeforeSnapshot,
    List<Cell> inputCellsAfterSnapshot) throws IOException {
    init(this.name.getMethodName() + "-" + inputCellsBeforeSnapshot.size());
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    long seqId = Long.MIN_VALUE;
    for (Cell c : inputCellsBeforeSnapshot) {
      quals.add(CellUtil.cloneQualifier(c));
      seqId = Math.max(seqId, c.getSequenceId());
    }
    for (Cell c : inputCellsAfterSnapshot) {
      quals.add(CellUtil.cloneQualifier(c));
      seqId = Math.max(seqId, c.getSequenceId());
    }
    inputCellsBeforeSnapshot.forEach(c -> store.add(c, null));
    StoreFlushContext storeFlushCtx = store.createFlushContext(id++, FlushLifeCycleTracker.DUMMY);
    storeFlushCtx.prepare();
    inputCellsAfterSnapshot.forEach(c -> store.add(c, null));
    int numberOfMemScannersBeforeFlush = inputCellsAfterSnapshot.isEmpty() ? 1 : 2;
    try (StoreScanner s = (StoreScanner) store.getScanner(new Scan(), quals, seqId)) {
      // snapshot + active (if inputCellsAfterSnapshot isn't empty)
      assertEquals(numberOfMemScannersBeforeFlush, countMemStoreScanner(s));
      storeFlushCtx.flushCache(Mockito.mock(MonitoredTask.class));
      storeFlushCtx.commit(Mockito.mock(MonitoredTask.class));
      // snapshot has no data after flush
      int numberOfMemScannersAfterFlush = inputCellsAfterSnapshot.isEmpty() ? 0 : 1;
      boolean more;
      int cellCount = 0;
      do {
        List<Cell> cells = new ArrayList<>();
        more = s.next(cells);
        cellCount += cells.size();
        assertEquals(more ? numberOfMemScannersAfterFlush : 0, countMemStoreScanner(s));
      } while (more);
      assertEquals(
        "The number of cells added before snapshot is " + inputCellsBeforeSnapshot.size()
          + ", The number of cells added after snapshot is " + inputCellsAfterSnapshot.size(),
        inputCellsBeforeSnapshot.size() + inputCellsAfterSnapshot.size(), cellCount);
      // the current scanners is cleared
      assertEquals(0, countMemStoreScanner(s));
    }
  }

  private Cell createCell(byte[] qualifier, long ts, long sequenceId, byte[] value)
    throws IOException {
    return createCell(row, qualifier, ts, sequenceId, value);
  }

  private Cell createCell(byte[] row, byte[] qualifier, long ts, long sequenceId, byte[] value)
    throws IOException {
    Cell c = CellBuilderFactory.create(CellBuilderType.DEEP_COPY).setRow(row).setFamily(family)
      .setQualifier(qualifier).setTimestamp(ts).setType(Cell.Type.Put).setValue(value).build();
    PrivateCellUtil.setSequenceId(c, sequenceId);
    return c;
  }

  @Test
  public void testFlushBeforeCompletingScanWoFilter() throws IOException, InterruptedException {
    final AtomicBoolean timeToGoNextRow = new AtomicBoolean(false);
    final int expectedSize = 3;
    testFlushBeforeCompletingScan(new MyListHook() {
      @Override
      public void hook(int currentSize) {
        if (currentSize == expectedSize - 1) {
          try {
            flushStore(store, id++);
            timeToGoNextRow.set(true);
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
      }
    }, new FilterBase() {
      @Override
      public Filter.ReturnCode filterCell(final Cell c) throws IOException {
        return ReturnCode.INCLUDE;
      }
    }, expectedSize);
  }

  @Test
  public void testFlushBeforeCompletingScanWithFilter() throws IOException, InterruptedException {
    final AtomicBoolean timeToGoNextRow = new AtomicBoolean(false);
    final int expectedSize = 2;
    testFlushBeforeCompletingScan(new MyListHook() {
      @Override
      public void hook(int currentSize) {
        if (currentSize == expectedSize - 1) {
          try {
            flushStore(store, id++);
            timeToGoNextRow.set(true);
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
      }
    }, new FilterBase() {
      @Override
      public Filter.ReturnCode filterCell(final Cell c) throws IOException {
        if (timeToGoNextRow.get()) {
          timeToGoNextRow.set(false);
          return ReturnCode.NEXT_ROW;
        } else {
          return ReturnCode.INCLUDE;
        }
      }
    }, expectedSize);
  }

  @Test
  public void testFlushBeforeCompletingScanWithFilterHint()
    throws IOException, InterruptedException {
    final AtomicBoolean timeToGetHint = new AtomicBoolean(false);
    final int expectedSize = 2;
    testFlushBeforeCompletingScan(new MyListHook() {
      @Override
      public void hook(int currentSize) {
        if (currentSize == expectedSize - 1) {
          try {
            flushStore(store, id++);
            timeToGetHint.set(true);
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
      }
    }, new FilterBase() {
      @Override
      public Filter.ReturnCode filterCell(final Cell c) throws IOException {
        if (timeToGetHint.get()) {
          timeToGetHint.set(false);
          return Filter.ReturnCode.SEEK_NEXT_USING_HINT;
        } else {
          return Filter.ReturnCode.INCLUDE;
        }
      }

      @Override
      public Cell getNextCellHint(Cell currentCell) throws IOException {
        return currentCell;
      }
    }, expectedSize);
  }

  private void testFlushBeforeCompletingScan(MyListHook hook, Filter filter, int expectedSize)
    throws IOException, InterruptedException {
    Configuration conf = HBaseConfiguration.create();
    byte[] r0 = Bytes.toBytes("row0");
    byte[] r1 = Bytes.toBytes("row1");
    byte[] r2 = Bytes.toBytes("row2");
    byte[] value0 = Bytes.toBytes("value0");
    byte[] value1 = Bytes.toBytes("value1");
    byte[] value2 = Bytes.toBytes("value2");
    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    init(name.getMethodName(), conf, TableDescriptorBuilder.newBuilder(TableName.valueOf(table)),
      ColumnFamilyDescriptorBuilder.newBuilder(family).setMaxVersions(1).build(),
      new MyStoreHook() {
        @Override
        public long getSmallestReadPoint(HStore store) {
          return seqId + 3;
        }
      });
    // The cells having the value0 won't be flushed to disk because the value of max version is 1
    store.add(createCell(r0, qf1, ts, seqId, value0), memStoreSizing);
    store.add(createCell(r0, qf2, ts, seqId, value0), memStoreSizing);
    store.add(createCell(r0, qf3, ts, seqId, value0), memStoreSizing);
    store.add(createCell(r1, qf1, ts + 1, seqId + 1, value1), memStoreSizing);
    store.add(createCell(r1, qf2, ts + 1, seqId + 1, value1), memStoreSizing);
    store.add(createCell(r1, qf3, ts + 1, seqId + 1, value1), memStoreSizing);
    store.add(createCell(r2, qf1, ts + 2, seqId + 2, value2), memStoreSizing);
    store.add(createCell(r2, qf2, ts + 2, seqId + 2, value2), memStoreSizing);
    store.add(createCell(r2, qf3, ts + 2, seqId + 2, value2), memStoreSizing);
    store.add(createCell(r1, qf1, ts + 3, seqId + 3, value1), memStoreSizing);
    store.add(createCell(r1, qf2, ts + 3, seqId + 3, value1), memStoreSizing);
    store.add(createCell(r1, qf3, ts + 3, seqId + 3, value1), memStoreSizing);
    List<Cell> myList = new MyList<>(hook);
    Scan scan = new Scan().withStartRow(r1).setFilter(filter);
    try (InternalScanner scanner = (InternalScanner) store.getScanner(scan, null, seqId + 3)) {
      // r1
      scanner.next(myList);
      assertEquals(expectedSize, myList.size());
      for (Cell c : myList) {
        byte[] actualValue = CellUtil.cloneValue(c);
        assertTrue("expected:" + Bytes.toStringBinary(value1) + ", actual:"
          + Bytes.toStringBinary(actualValue), Bytes.equals(actualValue, value1));
      }
      List<Cell> normalList = new ArrayList<>(3);
      // r2
      scanner.next(normalList);
      assertEquals(3, normalList.size());
      for (Cell c : normalList) {
        byte[] actualValue = CellUtil.cloneValue(c);
        assertTrue("expected:" + Bytes.toStringBinary(value2) + ", actual:"
          + Bytes.toStringBinary(actualValue), Bytes.equals(actualValue, value2));
      }
    }
  }

  @Test
  public void testCreateScannerAndSnapshotConcurrently() throws IOException, InterruptedException {
    Configuration conf = HBaseConfiguration.create();
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore.class.getName());
    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());
    byte[] value = Bytes.toBytes("value");
    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    // older data whihc shouldn't be "seen" by client
    store.add(createCell(qf1, ts, seqId, value), memStoreSizing);
    store.add(createCell(qf2, ts, seqId, value), memStoreSizing);
    store.add(createCell(qf3, ts, seqId, value), memStoreSizing);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);
    quals.add(qf3);
    StoreFlushContext storeFlushCtx = store.createFlushContext(id++, FlushLifeCycleTracker.DUMMY);
    MyCompactingMemStore.START_TEST.set(true);
    Runnable flush = () -> {
      // this is blocked until we create first scanner from pipeline and snapshot -- phase (1/5)
      // recreate the active memstore -- phase (4/5)
      storeFlushCtx.prepare();
    };
    ExecutorService service = Executors.newSingleThreadExecutor();
    service.execute(flush);
    // we get scanner from pipeline and snapshot but they are empty. -- phase (2/5)
    // this is blocked until we recreate the active memstore -- phase (3/5)
    // we get scanner from active memstore but it is empty -- phase (5/5)
    InternalScanner scanner =
      (InternalScanner) store.getScanner(new Scan(new Get(row)), quals, seqId + 1);
    service.shutdown();
    service.awaitTermination(20, TimeUnit.SECONDS);
    try {
      try {
        List<Cell> results = new ArrayList<>();
        scanner.next(results);
        assertEquals(3, results.size());
        for (Cell c : results) {
          byte[] actualValue = CellUtil.cloneValue(c);
          assertTrue("expected:" + Bytes.toStringBinary(value) + ", actual:"
            + Bytes.toStringBinary(actualValue), Bytes.equals(actualValue, value));
        }
      } finally {
        scanner.close();
      }
    } finally {
      MyCompactingMemStore.START_TEST.set(false);
      storeFlushCtx.flushCache(Mockito.mock(MonitoredTask.class));
      storeFlushCtx.commit(Mockito.mock(MonitoredTask.class));
    }
  }

  @Test
  public void testScanWithDoubleFlush() throws IOException {
    Configuration conf = HBaseConfiguration.create();
    // Initialize region
    MyStore myStore = initMyStore(name.getMethodName(), conf, new MyStoreHook() {
      @Override
      public void getScanners(MyStore store) throws IOException {
        final long tmpId = id++;
        ExecutorService s = Executors.newSingleThreadExecutor();
        s.execute(() -> {
          try {
            // flush the store before storescanner updates the scanners from store.
            // The current data will be flushed into files, and the memstore will
            // be clear.
            // -- phase (4/4)
            flushStore(store, tmpId);
          } catch (IOException ex) {
            throw new RuntimeException(ex);
          }
        });
        s.shutdown();
        try {
          // wait for the flush, the thread will be blocked in HStore#notifyChangedReadersObservers.
          s.awaitTermination(3, TimeUnit.SECONDS);
        } catch (InterruptedException ex) {
        }
      }
    });
    byte[] oldValue = Bytes.toBytes("oldValue");
    byte[] currentValue = Bytes.toBytes("currentValue");
    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    // older data whihc shouldn't be "seen" by client
    myStore.add(createCell(qf1, ts, seqId, oldValue), memStoreSizing);
    myStore.add(createCell(qf2, ts, seqId, oldValue), memStoreSizing);
    myStore.add(createCell(qf3, ts, seqId, oldValue), memStoreSizing);
    long snapshotId = id++;
    // push older data into snapshot -- phase (1/4)
    StoreFlushContext storeFlushCtx =
      store.createFlushContext(snapshotId, FlushLifeCycleTracker.DUMMY);
    storeFlushCtx.prepare();

    // insert current data into active -- phase (2/4)
    myStore.add(createCell(qf1, ts + 1, seqId + 1, currentValue), memStoreSizing);
    myStore.add(createCell(qf2, ts + 1, seqId + 1, currentValue), memStoreSizing);
    myStore.add(createCell(qf3, ts + 1, seqId + 1, currentValue), memStoreSizing);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);
    quals.add(qf3);
    try (InternalScanner scanner =
      (InternalScanner) myStore.getScanner(new Scan(new Get(row)), quals, seqId + 1)) {
      // complete the flush -- phase (3/4)
      storeFlushCtx.flushCache(Mockito.mock(MonitoredTask.class));
      storeFlushCtx.commit(Mockito.mock(MonitoredTask.class));

      List<Cell> results = new ArrayList<>();
      scanner.next(results);
      assertEquals(3, results.size());
      for (Cell c : results) {
        byte[] actualValue = CellUtil.cloneValue(c);
        assertTrue("expected:" + Bytes.toStringBinary(currentValue) + ", actual:"
          + Bytes.toStringBinary(actualValue), Bytes.equals(actualValue, currentValue));
      }
    }
  }

  /**
   * This test is for HBASE-27519, when the {@link StoreScanner} is scanning,the Flush and the
   * Compaction execute concurrently and theCcompaction compact and archive the flushed
   * {@link HStoreFile} which is used by {@link StoreScanner#updateReaders}.Before
   * HBASE-27519,{@link StoreScanner.updateReaders} would throw {@link FileNotFoundException}.
   */
  @Test
  public void testStoreScannerUpdateReadersWhenFlushAndCompactConcurrently() throws IOException {
    Configuration conf = HBaseConfiguration.create();
    conf.setBoolean(WALFactory.WAL_ENABLED, false);
    conf.set(DEFAULT_COMPACTION_POLICY_CLASS_KEY, EverythingPolicy.class.getName());
    byte[] r0 = Bytes.toBytes("row0");
    byte[] r1 = Bytes.toBytes("row1");
    final CyclicBarrier cyclicBarrier = new CyclicBarrier(2);
    final AtomicBoolean shouldWaitRef = new AtomicBoolean(false);
    // Initialize region
    final MyStore myStore = initMyStore(name.getMethodName(), conf, new MyStoreHook() {
      @Override
      public void getScanners(MyStore store) throws IOException {
        try {
          // Here this method is called by StoreScanner.updateReaders which is invoked by the
          // following TestHStore.flushStore
          if (shouldWaitRef.get()) {
            // wait the following compaction Task start
            cyclicBarrier.await();
            // wait the following HStore.closeAndArchiveCompactedFiles end.
            cyclicBarrier.await();
          }
        } catch (BrokenBarrierException | InterruptedException e) {
          throw new RuntimeException(e);
        }
      }
    });

    final AtomicReference<Throwable> compactionExceptionRef = new AtomicReference<Throwable>(null);
    Runnable compactionTask = () -> {
      try {
        // Only when the StoreScanner.updateReaders invoked by TestHStore.flushStore prepares for
        // entering the MyStore.getScanners, compactionTask could start.
        cyclicBarrier.await();
        region.compactStore(family, new NoLimitThroughputController());
        myStore.closeAndArchiveCompactedFiles();
        // Notify StoreScanner.updateReaders could enter MyStore.getScanners.
        cyclicBarrier.await();
      } catch (Throwable e) {
        compactionExceptionRef.set(e);
      }
    };

    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    byte[] value = Bytes.toBytes("value");
    // older data whihc shouldn't be "seen" by client
    myStore.add(createCell(r0, qf1, ts, seqId, value), null);
    flushStore(myStore, id++);
    myStore.add(createCell(r0, qf2, ts, seqId, value), null);
    flushStore(myStore, id++);
    myStore.add(createCell(r0, qf3, ts, seqId, value), null);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);
    quals.add(qf3);

    myStore.add(createCell(r1, qf1, ts, seqId, value), null);
    myStore.add(createCell(r1, qf2, ts, seqId, value), null);
    myStore.add(createCell(r1, qf3, ts, seqId, value), null);

    Thread.currentThread()
      .setName("testStoreScannerUpdateReadersWhenFlushAndCompactConcurrently thread");
    Scan scan = new Scan();
    scan.withStartRow(r0, true);
    try (InternalScanner scanner = (InternalScanner) myStore.getScanner(scan, quals, seqId)) {
      List<Cell> results = new MyList<>(size -> {
        switch (size) {
          case 1:
            shouldWaitRef.set(true);
            Thread thread = new Thread(compactionTask);
            thread.setName("MyCompacting Thread.");
            thread.start();
            try {
              flushStore(myStore, id++);
              thread.join();
            } catch (IOException | InterruptedException e) {
              throw new RuntimeException(e);
            }
            shouldWaitRef.set(false);
            break;
          default:
            break;
        }
      });
      // Before HBASE-27519, here would throw java.io.FileNotFoundException because the storeFile
      // which used by StoreScanner.updateReaders is deleted by compactionTask.
      scanner.next(results);
      // The results is r0 row cells.
      assertEquals(3, results.size());
      assertTrue(compactionExceptionRef.get() == null);
    }
  }

  @Test
  public void testReclaimChunkWhenScaning() throws IOException {
    init("testReclaimChunkWhenScaning");
    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    byte[] value = Bytes.toBytes("value");
    // older data whihc shouldn't be "seen" by client
    store.add(createCell(qf1, ts, seqId, value), null);
    store.add(createCell(qf2, ts, seqId, value), null);
    store.add(createCell(qf3, ts, seqId, value), null);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);
    quals.add(qf3);
    try (InternalScanner scanner =
      (InternalScanner) store.getScanner(new Scan(new Get(row)), quals, seqId)) {
      List<Cell> results = new MyList<>(size -> {
        switch (size) {
          // 1) we get the first cell (qf1)
          // 2) flush the data to have StoreScanner update inner scanners
          // 3) the chunk will be reclaimed after updaing
          case 1:
            try {
              flushStore(store, id++);
            } catch (IOException e) {
              throw new RuntimeException(e);
            }
            break;
          // 1) we get the second cell (qf2)
          // 2) add some cell to fill some byte into the chunk (we have only one chunk)
          case 2:
            try {
              byte[] newValue = Bytes.toBytes("newValue");
              // older data whihc shouldn't be "seen" by client
              store.add(createCell(qf1, ts + 1, seqId + 1, newValue), null);
              store.add(createCell(qf2, ts + 1, seqId + 1, newValue), null);
              store.add(createCell(qf3, ts + 1, seqId + 1, newValue), null);
            } catch (IOException e) {
              throw new RuntimeException(e);
            }
            break;
          default:
            break;
        }
      });
      scanner.next(results);
      assertEquals(3, results.size());
      for (Cell c : results) {
        byte[] actualValue = CellUtil.cloneValue(c);
        assertTrue("expected:" + Bytes.toStringBinary(value) + ", actual:"
          + Bytes.toStringBinary(actualValue), Bytes.equals(actualValue, value));
      }
    }
  }

  /**
   * If there are two running InMemoryFlushRunnable, the later InMemoryFlushRunnable may change the
   * versionedList. And the first InMemoryFlushRunnable will use the chagned versionedList to remove
   * the corresponding segments. In short, there will be some segements which isn't in merge are
   * removed.
   */
  @Test
  public void testRunDoubleMemStoreCompactors() throws IOException, InterruptedException {
    int flushSize = 500;
    Configuration conf = HBaseConfiguration.create();
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStoreWithCustomCompactor.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.25);
    MyCompactingMemStoreWithCustomCompactor.RUNNER_COUNT.set(0);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushSize));
    // Set the lower threshold to invoke the "MERGE" policy
    conf.set(MemStoreCompactionStrategy.COMPACTING_MEMSTORE_THRESHOLD_KEY, String.valueOf(0));
    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());
    byte[] value = Bytes.toBytes("thisisavarylargevalue");
    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long ts = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    // older data whihc shouldn't be "seen" by client
    store.add(createCell(qf1, ts, seqId, value), memStoreSizing);
    store.add(createCell(qf2, ts, seqId, value), memStoreSizing);
    store.add(createCell(qf3, ts, seqId, value), memStoreSizing);
    assertEquals(1, MyCompactingMemStoreWithCustomCompactor.RUNNER_COUNT.get());
    StoreFlushContext storeFlushCtx = store.createFlushContext(id++, FlushLifeCycleTracker.DUMMY);
    storeFlushCtx.prepare();
    // This shouldn't invoke another in-memory flush because the first compactor thread
    // hasn't accomplished the in-memory compaction.
    store.add(createCell(qf1, ts + 1, seqId + 1, value), memStoreSizing);
    store.add(createCell(qf1, ts + 1, seqId + 1, value), memStoreSizing);
    store.add(createCell(qf1, ts + 1, seqId + 1, value), memStoreSizing);
    assertEquals(1, MyCompactingMemStoreWithCustomCompactor.RUNNER_COUNT.get());
    // okay. Let the compaction be completed
    MyMemStoreCompactor.START_COMPACTOR_LATCH.countDown();
    CompactingMemStore mem = (CompactingMemStore) ((HStore) store).memstore;
    while (mem.isMemStoreFlushingInMemory()) {
      TimeUnit.SECONDS.sleep(1);
    }
    // This should invoke another in-memory flush.
    store.add(createCell(qf1, ts + 2, seqId + 2, value), memStoreSizing);
    store.add(createCell(qf1, ts + 2, seqId + 2, value), memStoreSizing);
    store.add(createCell(qf1, ts + 2, seqId + 2, value), memStoreSizing);
    assertEquals(2, MyCompactingMemStoreWithCustomCompactor.RUNNER_COUNT.get());
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE,
      String.valueOf(TableDescriptorBuilder.DEFAULT_MEMSTORE_FLUSH_SIZE));
    storeFlushCtx.flushCache(Mockito.mock(MonitoredTask.class));
    storeFlushCtx.commit(Mockito.mock(MonitoredTask.class));
  }

  @Test
  public void testAge() throws IOException {
    long currentTime = EnvironmentEdgeManager.currentTime();
    ManualEnvironmentEdge edge = new ManualEnvironmentEdge();
    edge.setValue(currentTime);
    EnvironmentEdgeManager.injectEdge(edge);
    Configuration conf = TEST_UTIL.getConfiguration();
    ColumnFamilyDescriptor hcd = ColumnFamilyDescriptorBuilder.of(family);
    initHRegion(name.getMethodName(), conf,
      TableDescriptorBuilder.newBuilder(TableName.valueOf(table)), hcd, null, false);
    HStore store = new HStore(region, hcd, conf, false) {

      @Override
      protected StoreEngine<?, ?, ?, ?> createStoreEngine(HStore store, Configuration conf,
        CellComparator kvComparator) throws IOException {
        List<HStoreFile> storefiles =
          Arrays.asList(mockStoreFile(currentTime - 10), mockStoreFile(currentTime - 100),
            mockStoreFile(currentTime - 1000), mockStoreFile(currentTime - 10000));
        StoreFileManager sfm = mock(StoreFileManager.class);
        when(sfm.getStorefiles()).thenReturn(storefiles);
        StoreEngine<?, ?, ?, ?> storeEngine = mock(StoreEngine.class);
        when(storeEngine.getStoreFileManager()).thenReturn(sfm);
        return storeEngine;
      }
    };
    assertEquals(10L, store.getMinStoreFileAge().getAsLong());
    assertEquals(10000L, store.getMaxStoreFileAge().getAsLong());
    assertEquals((10 + 100 + 1000 + 10000) / 4.0, store.getAvgStoreFileAge().getAsDouble(), 1E-4);
  }

  private HStoreFile mockStoreFile(long createdTime) {
    StoreFileInfo info = mock(StoreFileInfo.class);
    when(info.getCreatedTimestamp()).thenReturn(createdTime);
    HStoreFile sf = mock(HStoreFile.class);
    when(sf.getReader()).thenReturn(mock(StoreFileReader.class));
    when(sf.isHFile()).thenReturn(true);
    when(sf.getFileInfo()).thenReturn(info);
    return sf;
  }

  private MyStore initMyStore(String methodName, Configuration conf, MyStoreHook hook)
    throws IOException {
    return (MyStore) init(methodName, conf,
      TableDescriptorBuilder.newBuilder(TableName.valueOf(table)),
      ColumnFamilyDescriptorBuilder.newBuilder(family).setMaxVersions(5).build(), hook);
  }

  private static class MyStore extends HStore {
    private final MyStoreHook hook;

    MyStore(final HRegion region, final ColumnFamilyDescriptor family,
      final Configuration confParam, MyStoreHook hook, boolean switchToPread) throws IOException {
      super(region, family, confParam, false);
      this.hook = hook;
    }

    @Override
    public List<KeyValueScanner> getScanners(List<HStoreFile> files, boolean cacheBlocks,
      boolean usePread, boolean isCompaction, ScanQueryMatcher matcher, byte[] startRow,
      boolean includeStartRow, byte[] stopRow, boolean includeStopRow, long readPt,
      boolean includeMemstoreScanner) throws IOException {
      hook.getScanners(this);
      return super.getScanners(files, cacheBlocks, usePread, isCompaction, matcher, startRow, true,
        stopRow, false, readPt, includeMemstoreScanner);
    }

    @Override
    public long getSmallestReadPoint() {
      return hook.getSmallestReadPoint(this);
    }
  }

  private abstract static class MyStoreHook {

    void getScanners(MyStore store) throws IOException {
    }

    long getSmallestReadPoint(HStore store) {
      return store.getHRegion().getSmallestReadPoint();
    }
  }

  @Test
  public void testSwitchingPreadtoStreamParallelyWithCompactionDischarger() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    conf.set("hbase.hstore.engine.class", DummyStoreEngine.class.getName());
    conf.setLong(StoreScanner.STORESCANNER_PREAD_MAX_BYTES, 0);
    // Set the lower threshold to invoke the "MERGE" policy
    MyStore store = initMyStore(name.getMethodName(), conf, new MyStoreHook() {
    });
    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long ts = EnvironmentEdgeManager.currentTime();
    long seqID = 1L;
    // Add some data to the region and do some flushes
    for (int i = 1; i < 10; i++) {
      store.add(createCell(Bytes.toBytes("row" + i), qf1, ts, seqID++, Bytes.toBytes("")),
        memStoreSizing);
    }
    // flush them
    flushStore(store, seqID);
    for (int i = 11; i < 20; i++) {
      store.add(createCell(Bytes.toBytes("row" + i), qf1, ts, seqID++, Bytes.toBytes("")),
        memStoreSizing);
    }
    // flush them
    flushStore(store, seqID);
    for (int i = 21; i < 30; i++) {
      store.add(createCell(Bytes.toBytes("row" + i), qf1, ts, seqID++, Bytes.toBytes("")),
        memStoreSizing);
    }
    // flush them
    flushStore(store, seqID);

    assertEquals(3, store.getStorefilesCount());
    Scan scan = new Scan();
    scan.addFamily(family);
    Collection<HStoreFile> storefiles2 = store.getStorefiles();
    ArrayList<HStoreFile> actualStorefiles = Lists.newArrayList(storefiles2);
    StoreScanner storeScanner =
      (StoreScanner) store.getScanner(scan, scan.getFamilyMap().get(family), Long.MAX_VALUE);
    // get the current heap
    KeyValueHeap heap = storeScanner.heap;
    // create more store files
    for (int i = 31; i < 40; i++) {
      store.add(createCell(Bytes.toBytes("row" + i), qf1, ts, seqID++, Bytes.toBytes("")),
        memStoreSizing);
    }
    // flush them
    flushStore(store, seqID);

    for (int i = 41; i < 50; i++) {
      store.add(createCell(Bytes.toBytes("row" + i), qf1, ts, seqID++, Bytes.toBytes("")),
        memStoreSizing);
    }
    // flush them
    flushStore(store, seqID);
    storefiles2 = store.getStorefiles();
    ArrayList<HStoreFile> actualStorefiles1 = Lists.newArrayList(storefiles2);
    actualStorefiles1.removeAll(actualStorefiles);
    // Do compaction
    MyThread thread = new MyThread(storeScanner);
    thread.start();
    store.replaceStoreFiles(actualStorefiles, actualStorefiles1, false);
    thread.join();
    KeyValueHeap heap2 = thread.getHeap();
    assertFalse(heap.equals(heap2));
  }

  @Test
  public void testMaxPreadBytesConfiguredToBeLessThanZero() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    conf.set("hbase.hstore.engine.class", DummyStoreEngine.class.getName());
    // Set 'hbase.storescanner.pread.max.bytes' < 0, so that StoreScanner will be a STREAM type.
    conf.setLong(StoreScanner.STORESCANNER_PREAD_MAX_BYTES, -1);
    MyStore store = initMyStore(name.getMethodName(), conf, new MyStoreHook() {
    });
    Scan scan = new Scan();
    scan.addFamily(family);
    // ReadType on Scan is still DEFAULT only.
    assertEquals(ReadType.DEFAULT, scan.getReadType());
    StoreScanner storeScanner =
      (StoreScanner) store.getScanner(scan, scan.getFamilyMap().get(family), Long.MAX_VALUE);
    assertFalse(storeScanner.isScanUsePread());
  }

  @Test
  public void testSpaceQuotaChangeAfterReplacement() throws IOException {
    final TableName tn = TableName.valueOf(name.getMethodName());
    init(name.getMethodName());

    RegionSizeStoreImpl sizeStore = new RegionSizeStoreImpl();

    HStoreFile sf1 = mockStoreFileWithLength(1024L);
    HStoreFile sf2 = mockStoreFileWithLength(2048L);
    HStoreFile sf3 = mockStoreFileWithLength(4096L);
    HStoreFile sf4 = mockStoreFileWithLength(8192L);

    RegionInfo regionInfo = RegionInfoBuilder.newBuilder(tn).setStartKey(Bytes.toBytes("a"))
      .setEndKey(Bytes.toBytes("b")).build();

    // Compacting two files down to one, reducing size
    sizeStore.put(regionInfo, 1024L + 4096L);
    store.updateSpaceQuotaAfterFileReplacement(sizeStore, regionInfo, Arrays.asList(sf1, sf3),
      Arrays.asList(sf2));

    assertEquals(2048L, sizeStore.getRegionSize(regionInfo).getSize());

    // The same file length in and out should have no change
    store.updateSpaceQuotaAfterFileReplacement(sizeStore, regionInfo, Arrays.asList(sf2),
      Arrays.asList(sf2));

    assertEquals(2048L, sizeStore.getRegionSize(regionInfo).getSize());

    // Increase the total size used
    store.updateSpaceQuotaAfterFileReplacement(sizeStore, regionInfo, Arrays.asList(sf2),
      Arrays.asList(sf3));

    assertEquals(4096L, sizeStore.getRegionSize(regionInfo).getSize());

    RegionInfo regionInfo2 = RegionInfoBuilder.newBuilder(tn).setStartKey(Bytes.toBytes("b"))
      .setEndKey(Bytes.toBytes("c")).build();
    store.updateSpaceQuotaAfterFileReplacement(sizeStore, regionInfo2, null, Arrays.asList(sf4));

    assertEquals(8192L, sizeStore.getRegionSize(regionInfo2).getSize());
  }

  @Test
  public void testHFileContextSetWithCFAndTable() throws Exception {
    init(this.name.getMethodName());
    StoreFileWriter writer = store.getStoreEngine()
      .createWriter(CreateStoreFileWriterParams.create().maxKeyCount(10000L)
        .compression(Compression.Algorithm.NONE).isCompaction(true).includeMVCCReadpoint(true)
        .includesTag(false).shouldDropBehind(true));
    HFileContext hFileContext = writer.getHFileWriter().getFileContext();
    assertArrayEquals(family, hFileContext.getColumnFamily());
    assertArrayEquals(table, hFileContext.getTableName());
  }

  // This test is for HBASE-26026, HBase Write be stuck when active segment has no cell
  // but its dataSize exceeds inmemoryFlushSize
  @Test
  public void testCompactingMemStoreNoCellButDataSizeExceedsInmemoryFlushSize()
    throws IOException, InterruptedException {
    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    int smallCellByteSize = MutableSegment.getCellLength(smallCell);
    int largeCellByteSize = MutableSegment.getCellLength(largeCell);
    int flushByteSize = smallCellByteSize + largeCellByteSize - 2;

    // set CompactingMemStore.inmemoryFlushSize to flushByteSize.
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore2.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushByteSize * 200));

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    MyCompactingMemStore2 myCompactingMemStore = ((MyCompactingMemStore2) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == flushByteSize);
    myCompactingMemStore.smallCellPreUpdateCounter.set(0);
    myCompactingMemStore.largeCellPreUpdateCounter.set(0);

    final AtomicReference<Throwable> exceptionRef = new AtomicReference<Throwable>();
    Thread smallCellThread = new Thread(() -> {
      try {
        store.add(smallCell, new NonThreadSafeMemStoreSizing());
      } catch (Throwable exception) {
        exceptionRef.set(exception);
      }
    });
    smallCellThread.setName(MyCompactingMemStore2.SMALL_CELL_THREAD_NAME);
    smallCellThread.start();

    String oldThreadName = Thread.currentThread().getName();
    try {
      /**
       * 1.smallCellThread enters CompactingMemStore.checkAndAddToActiveSize first, then
       * largeCellThread enters CompactingMemStore.checkAndAddToActiveSize, and then largeCellThread
       * invokes flushInMemory.
       * <p/>
       * 2. After largeCellThread finished CompactingMemStore.flushInMemory method, smallCellThread
       * can add cell to currentActive . That is to say when largeCellThread called flushInMemory
       * method, CompactingMemStore.active has no cell.
       */
      Thread.currentThread().setName(MyCompactingMemStore2.LARGE_CELL_THREAD_NAME);
      store.add(largeCell, new NonThreadSafeMemStoreSizing());
      smallCellThread.join();

      for (int i = 0; i < 100; i++) {
        long currentTimestamp = timestamp + 100 + i;
        Cell cell = createCell(qf2, currentTimestamp, seqId, largeValue);
        store.add(cell, new NonThreadSafeMemStoreSizing());
      }
    } finally {
      Thread.currentThread().setName(oldThreadName);
    }

    assertTrue(exceptionRef.get() == null);

  }

  // This test is for HBASE-26210, HBase Write be stuck when there is cell which size exceeds
  // InmemoryFlushSize
  @Test(timeout = 60000)
  public void testCompactingMemStoreCellExceedInmemoryFlushSize() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore6.class.getName());

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    MyCompactingMemStore6 myCompactingMemStore = ((MyCompactingMemStore6) store.memstore);

    int size = (int) (myCompactingMemStore.getInmemoryFlushSize());
    byte[] value = new byte[size + 1];

    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    long timestamp = EnvironmentEdgeManager.currentTime();
    long seqId = 100;
    Cell cell = createCell(qf1, timestamp, seqId, value);
    int cellByteSize = MutableSegment.getCellLength(cell);
    store.add(cell, memStoreSizing);
    assertTrue(memStoreSizing.getCellsCount() == 1);
    assertTrue(memStoreSizing.getDataSize() == cellByteSize);
    // Waiting the in memory compaction completed, see HBASE-26438
    myCompactingMemStore.inMemoryCompactionEndCyclicBarrier.await();
  }

  /**
   * This test is for HBASE-27464, before this JIRA,when init {@link CellChunkImmutableSegment} for
   * 'COMPACT' action, we not force copy to current MSLab. When cell size bigger than
   * {@link MemStoreLABImpl#maxAlloc}, cell will stay in previous chunk which will recycle after
   * segment replace, and we may read wrong data when these chunk reused by others.
   */
  @Test
  public void testForceCloneOfBigCellForCellChunkImmutableSegment() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    int maxAllocByteSize = conf.getInt(MemStoreLAB.MAX_ALLOC_KEY, MemStoreLAB.MAX_ALLOC_DEFAULT);

    // Construct big cell,which is large than {@link MemStoreLABImpl#maxAlloc}.
    byte[] cellValue = new byte[maxAllocByteSize + 1];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final byte[] rowKey1 = Bytes.toBytes("rowKey1");
    final Cell originalCell1 = createCell(rowKey1, qf1, timestamp, seqId, cellValue);
    final byte[] rowKey2 = Bytes.toBytes("rowKey2");
    final Cell originalCell2 = createCell(rowKey2, qf1, timestamp, seqId, cellValue);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);

    int cellByteSize = MutableSegment.getCellLength(originalCell1);
    int inMemoryFlushByteSize = cellByteSize - 1;

    // set CompactingMemStore.inmemoryFlushSize to flushByteSize.
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore6.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(inMemoryFlushByteSize * 200));
    conf.setBoolean(WALFactory.WAL_ENABLED, false);

    // Use {@link MemoryCompactionPolicy#EAGER} for always compacting.
    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.EAGER).build());

    MyCompactingMemStore6 myCompactingMemStore = ((MyCompactingMemStore6) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == inMemoryFlushByteSize);

    // Data chunk Pool is disabled.
    assertTrue(ChunkCreator.getInstance().getMaxCount(ChunkType.DATA_CHUNK) == 0);

    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();

    // First compact
    store.add(originalCell1, memStoreSizing);
    // Waiting for the first in-memory compaction finished
    myCompactingMemStore.inMemoryCompactionEndCyclicBarrier.await();

    StoreScanner storeScanner =
      (StoreScanner) store.getScanner(new Scan(new Get(rowKey1)), quals, seqId + 1);
    SegmentScanner segmentScanner = getTypeKeyValueScanner(storeScanner, SegmentScanner.class);
    Cell resultCell1 = segmentScanner.next();
    assertTrue(CellUtil.equals(resultCell1, originalCell1));
    int cell1ChunkId = ((ExtendedCell) resultCell1).getChunkId();
    assertTrue(cell1ChunkId != ExtendedCell.CELL_NOT_BASED_ON_CHUNK);
    assertNull(segmentScanner.next());
    segmentScanner.close();
    storeScanner.close();
    Segment segment = segmentScanner.segment;
    assertTrue(segment instanceof CellChunkImmutableSegment);
    MemStoreLABImpl memStoreLAB1 = (MemStoreLABImpl) (segmentScanner.segment.getMemStoreLAB());
    assertTrue(!memStoreLAB1.isClosed());
    assertTrue(!memStoreLAB1.chunks.isEmpty());
    assertTrue(!memStoreLAB1.isReclaimed());

    // Second compact
    store.add(originalCell2, memStoreSizing);
    // Waiting for the second in-memory compaction finished
    myCompactingMemStore.inMemoryCompactionEndCyclicBarrier.await();

    // Before HBASE-27464, here may throw java.lang.IllegalArgumentException: In CellChunkMap, cell
    // must be associated with chunk.. We were looking for a cell at index 0.
    // The cause for this exception is because the data chunk Pool is disabled,when the data chunks
    // are recycled after the second in-memory compaction finished,the
    // {@link ChunkCreator.putbackChunks} method does not put the chunks back to the data chunk
    // pool,it just removes them from {@link ChunkCreator#chunkIdMap},so in
    // {@link CellChunkMap#getCell} we could not get the data chunk by chunkId.
    storeScanner = (StoreScanner) store.getScanner(new Scan(new Get(rowKey1)), quals, seqId + 1);
    segmentScanner = getTypeKeyValueScanner(storeScanner, SegmentScanner.class);
    Cell newResultCell1 = segmentScanner.next();
    assertTrue(newResultCell1 != resultCell1);
    assertTrue(CellUtil.equals(newResultCell1, originalCell1));

    Cell resultCell2 = segmentScanner.next();
    assertTrue(CellUtil.equals(resultCell2, originalCell2));
    assertNull(segmentScanner.next());
    segmentScanner.close();
    storeScanner.close();

    segment = segmentScanner.segment;
    assertTrue(segment instanceof CellChunkImmutableSegment);
    MemStoreLABImpl memStoreLAB2 = (MemStoreLABImpl) (segmentScanner.segment.getMemStoreLAB());
    assertTrue(!memStoreLAB2.isClosed());
    assertTrue(!memStoreLAB2.chunks.isEmpty());
    assertTrue(!memStoreLAB2.isReclaimed());
    assertTrue(memStoreLAB1.isClosed());
    assertTrue(memStoreLAB1.chunks.isEmpty());
    assertTrue(memStoreLAB1.isReclaimed());
  }

  // This test is for HBASE-26210 also, test write large cell and small cell concurrently when
  // InmemoryFlushSize is smaller,equal with and larger than cell size.
  @Test
  public void testCompactingMemStoreWriteLargeCellAndSmallCellConcurrently()
    throws IOException, InterruptedException {
    doWriteTestLargeCellAndSmallCellConcurrently(
      (smallCellByteSize, largeCellByteSize) -> largeCellByteSize - 1);
    doWriteTestLargeCellAndSmallCellConcurrently(
      (smallCellByteSize, largeCellByteSize) -> largeCellByteSize);
    doWriteTestLargeCellAndSmallCellConcurrently(
      (smallCellByteSize, largeCellByteSize) -> smallCellByteSize + largeCellByteSize - 1);
    doWriteTestLargeCellAndSmallCellConcurrently(
      (smallCellByteSize, largeCellByteSize) -> smallCellByteSize + largeCellByteSize);
    doWriteTestLargeCellAndSmallCellConcurrently(
      (smallCellByteSize, largeCellByteSize) -> smallCellByteSize + largeCellByteSize + 1);
  }

  private void doWriteTestLargeCellAndSmallCellConcurrently(IntBinaryOperator getFlushByteSize)
    throws IOException, InterruptedException {

    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[100];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    int smallCellByteSize = MutableSegment.getCellLength(smallCell);
    int largeCellByteSize = MutableSegment.getCellLength(largeCell);
    int flushByteSize = getFlushByteSize.applyAsInt(smallCellByteSize, largeCellByteSize);
    boolean flushByteSizeLessThanSmallAndLargeCellSize =
      flushByteSize < (smallCellByteSize + largeCellByteSize);

    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore3.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushByteSize * 200));

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    MyCompactingMemStore3 myCompactingMemStore = ((MyCompactingMemStore3) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == flushByteSize);
    myCompactingMemStore.disableCompaction();
    if (flushByteSizeLessThanSmallAndLargeCellSize) {
      myCompactingMemStore.flushByteSizeLessThanSmallAndLargeCellSize = true;
    } else {
      myCompactingMemStore.flushByteSizeLessThanSmallAndLargeCellSize = false;
    }

    final ThreadSafeMemStoreSizing memStoreSizing = new ThreadSafeMemStoreSizing();
    final AtomicLong totalCellByteSize = new AtomicLong(0);
    final AtomicReference<Throwable> exceptionRef = new AtomicReference<Throwable>();
    Thread smallCellThread = new Thread(() -> {
      try {
        for (int i = 1; i <= MyCompactingMemStore3.CELL_COUNT; i++) {
          long currentTimestamp = timestamp + i;
          Cell cell = createCell(qf1, currentTimestamp, seqId, smallValue);
          totalCellByteSize.addAndGet(MutableSegment.getCellLength(cell));
          store.add(cell, memStoreSizing);
        }
      } catch (Throwable exception) {
        exceptionRef.set(exception);

      }
    });
    smallCellThread.setName(MyCompactingMemStore3.SMALL_CELL_THREAD_NAME);
    smallCellThread.start();

    String oldThreadName = Thread.currentThread().getName();
    try {
      /**
       * When flushByteSizeLessThanSmallAndLargeCellSize is true:
       * </p>
       * 1.smallCellThread enters MyCompactingMemStore3.checkAndAddToActiveSize first, then
       * largeCellThread enters MyCompactingMemStore3.checkAndAddToActiveSize, and then
       * largeCellThread invokes flushInMemory.
       * <p/>
       * 2. After largeCellThread finished CompactingMemStore.flushInMemory method, smallCellThread
       * can run into MyCompactingMemStore3.checkAndAddToActiveSize again.
       * <p/>
       * When flushByteSizeLessThanSmallAndLargeCellSize is false: smallCellThread and
       * largeCellThread concurrently write one cell and wait each other, and then write another
       * cell etc.
       */
      Thread.currentThread().setName(MyCompactingMemStore3.LARGE_CELL_THREAD_NAME);
      for (int i = 1; i <= MyCompactingMemStore3.CELL_COUNT; i++) {
        long currentTimestamp = timestamp + i;
        Cell cell = createCell(qf2, currentTimestamp, seqId, largeValue);
        totalCellByteSize.addAndGet(MutableSegment.getCellLength(cell));
        store.add(cell, memStoreSizing);
      }
      smallCellThread.join();

      assertTrue(exceptionRef.get() == null);
      assertTrue(memStoreSizing.getCellsCount() == (MyCompactingMemStore3.CELL_COUNT * 2));
      assertTrue(memStoreSizing.getDataSize() == totalCellByteSize.get());
      if (flushByteSizeLessThanSmallAndLargeCellSize) {
        assertTrue(myCompactingMemStore.flushCounter.get() == MyCompactingMemStore3.CELL_COUNT);
      } else {
        assertTrue(
          myCompactingMemStore.flushCounter.get() <= (MyCompactingMemStore3.CELL_COUNT - 1));
      }
    } finally {
      Thread.currentThread().setName(oldThreadName);
    }
  }

  /**
   * <pre>
   * This test is for HBASE-26384,
   * test {@link CompactingMemStore#flattenOneSegment} and {@link CompactingMemStore#snapshot()}
   * execute concurrently.
   * The threads sequence before HBASE-26384 is(The bug only exists for branch-2,and I add UTs
   * for both branch-2 and master):
   * 1. The {@link CompactingMemStore} size exceeds
   *    {@link CompactingMemStore#getInmemoryFlushSize()},the write thread adds a new
   *    {@link ImmutableSegment}  to the head of {@link CompactingMemStore#pipeline},and start a
   *    in memory compact thread to execute {@link CompactingMemStore#inMemoryCompaction}.
   * 2. The in memory compact thread starts and then stopping before
   *    {@link CompactingMemStore#flattenOneSegment}.
   * 3. The snapshot thread starts {@link CompactingMemStore#snapshot} concurrently,after the
   *    snapshot thread executing {@link CompactingMemStore#getImmutableSegments},the in memory
   *    compact thread continues.
   *    Assuming {@link VersionedSegmentsList#version} returned from
   *    {@link CompactingMemStore#getImmutableSegments} is v.
   * 4. The snapshot thread stopping before {@link CompactingMemStore#swapPipelineWithNull}.
   * 5. The in memory compact thread completes {@link CompactingMemStore#flattenOneSegment},
   *    {@link CompactionPipeline#version} is still v.
   * 6. The snapshot thread continues {@link CompactingMemStore#swapPipelineWithNull}, and because
   *    {@link CompactionPipeline#version} is v, {@link CompactingMemStore#swapPipelineWithNull}
   *    thinks it is successful and continue flushing,but the {@link ImmutableSegment} in
   *    {@link CompactionPipeline} has changed because
   *    {@link CompactingMemStore#flattenOneSegment},so the {@link ImmutableSegment} is not
   *    removed in fact and still remaining in {@link CompactionPipeline}.
   *
   * After HBASE-26384, the 5-6 step is changed to following, which is expected behavior:
   * 5. The in memory compact thread completes {@link CompactingMemStore#flattenOneSegment},
   *    {@link CompactingMemStore#flattenOneSegment} change {@link CompactionPipeline#version} to
   *    v+1.
   * 6. The snapshot thread continues {@link CompactingMemStore#swapPipelineWithNull}, and because
   *    {@link CompactionPipeline#version} is v+1, {@link CompactingMemStore#swapPipelineWithNull}
   *    failed and retry the while loop in {@link CompactingMemStore#pushPipelineToSnapshot} once
   *    again, because there is no concurrent {@link CompactingMemStore#inMemoryCompaction} now,
   *    {@link CompactingMemStore#swapPipelineWithNull} succeeds.
   * </pre>
   */
  @Test
  public void testFlattenAndSnapshotCompactingMemStoreConcurrently() throws Exception {
    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    int smallCellByteSize = MutableSegment.getCellLength(smallCell);
    int largeCellByteSize = MutableSegment.getCellLength(largeCell);
    int totalCellByteSize = (smallCellByteSize + largeCellByteSize);
    int flushByteSize = totalCellByteSize - 2;

    // set CompactingMemStore.inmemoryFlushSize to flushByteSize.
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore4.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushByteSize * 200));

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    MyCompactingMemStore4 myCompactingMemStore = ((MyCompactingMemStore4) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == flushByteSize);

    store.add(smallCell, new NonThreadSafeMemStoreSizing());
    store.add(largeCell, new NonThreadSafeMemStoreSizing());

    String oldThreadName = Thread.currentThread().getName();
    try {
      Thread.currentThread().setName(MyCompactingMemStore4.TAKE_SNAPSHOT_THREAD_NAME);
      /**
       * {@link CompactingMemStore#snapshot} must wait the in memory compact thread enters
       * {@link CompactingMemStore#flattenOneSegment},because {@link CompactingMemStore#snapshot}
       * would invoke {@link CompactingMemStore#stopCompaction}.
       */
      myCompactingMemStore.snapShotStartCyclicCyclicBarrier.await();

      MemStoreSnapshot memStoreSnapshot = myCompactingMemStore.snapshot();
      myCompactingMemStore.inMemoryCompactionEndCyclicBarrier.await();

      assertTrue(memStoreSnapshot.getCellsCount() == 2);
      assertTrue(((int) (memStoreSnapshot.getDataSize())) == totalCellByteSize);
      VersionedSegmentsList segments = myCompactingMemStore.getImmutableSegments();
      assertTrue(segments.getNumOfSegments() == 0);
      assertTrue(segments.getNumOfCells() == 0);
      assertTrue(myCompactingMemStore.setInMemoryCompactionFlagCounter.get() == 1);
      assertTrue(myCompactingMemStore.swapPipelineWithNullCounter.get() == 2);
    } finally {
      Thread.currentThread().setName(oldThreadName);
    }
  }

  /**
   * <pre>
   * This test is for HBASE-26384,
   * test {@link CompactingMemStore#flattenOneSegment}{@link CompactingMemStore#snapshot()}
   * and writeMemStore execute concurrently.
   * The threads sequence before HBASE-26384 is(The bug only exists for branch-2,and I add UTs
   * for both branch-2 and master):
   * 1. The {@link CompactingMemStore} size exceeds
   *    {@link CompactingMemStore#getInmemoryFlushSize()},the write thread adds a new
   *    {@link ImmutableSegment}  to the head of {@link CompactingMemStore#pipeline},and start a
   *    in memory compact thread to execute {@link CompactingMemStore#inMemoryCompaction}.
   * 2. The in memory compact thread starts and then stopping before
   *    {@link CompactingMemStore#flattenOneSegment}.
   * 3. The snapshot thread starts {@link CompactingMemStore#snapshot} concurrently,after the
   *    snapshot thread executing {@link CompactingMemStore#getImmutableSegments},the in memory
   *    compact thread continues.
   *    Assuming {@link VersionedSegmentsList#version} returned from
   *    {@link CompactingMemStore#getImmutableSegments} is v.
   * 4. The snapshot thread stopping before {@link CompactingMemStore#swapPipelineWithNull}.
   * 5. The in memory compact thread completes {@link CompactingMemStore#flattenOneSegment},
   *    {@link CompactionPipeline#version} is still v.
   * 6. The snapshot thread continues {@link CompactingMemStore#swapPipelineWithNull}, and because
   *    {@link CompactionPipeline#version} is v, {@link CompactingMemStore#swapPipelineWithNull}
   *    thinks it is successful and continue flushing,but the {@link ImmutableSegment} in
   *    {@link CompactionPipeline} has changed because
   *    {@link CompactingMemStore#flattenOneSegment},so the {@link ImmutableSegment} is not
   *    removed in fact and still remaining in {@link CompactionPipeline}.
   *
   * After HBASE-26384, the 5-6 step is changed to following, which is expected behavior,
   * and I add step 7-8 to test there is new segment added before retry.
   * 5. The in memory compact thread completes {@link CompactingMemStore#flattenOneSegment},
   *    {@link CompactingMemStore#flattenOneSegment} change {@link CompactionPipeline#version} to
   *     v+1.
   * 6. The snapshot thread continues {@link CompactingMemStore#swapPipelineWithNull}, and because
   *    {@link CompactionPipeline#version} is v+1, {@link CompactingMemStore#swapPipelineWithNull}
   *    failed and retry,{@link VersionedSegmentsList#version} returned from
   *    {@link CompactingMemStore#getImmutableSegments} is v+1.
   * 7. The write thread continues writing to {@link CompactingMemStore} and
   *    {@link CompactingMemStore} size exceeds {@link CompactingMemStore#getInmemoryFlushSize()},
   *    {@link CompactingMemStore#flushInMemory(MutableSegment)} is called and a new
   *    {@link ImmutableSegment} is added to the head of {@link CompactingMemStore#pipeline},
   *    {@link CompactionPipeline#version} is still v+1.
   * 8. The snapshot thread continues {@link CompactingMemStore#swapPipelineWithNull}, and because
   *    {@link CompactionPipeline#version} is still v+1,
   *    {@link CompactingMemStore#swapPipelineWithNull} succeeds.The new {@link ImmutableSegment}
   *    remained at the head of {@link CompactingMemStore#pipeline},the old is removed by
   *    {@link CompactingMemStore#swapPipelineWithNull}.
   * </pre>
   */
  @Test
  public void testFlattenSnapshotWriteCompactingMemeStoreConcurrently() throws Exception {
    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    int smallCellByteSize = MutableSegment.getCellLength(smallCell);
    int largeCellByteSize = MutableSegment.getCellLength(largeCell);
    int firstWriteCellByteSize = (smallCellByteSize + largeCellByteSize);
    int flushByteSize = firstWriteCellByteSize - 2;

    // set CompactingMemStore.inmemoryFlushSize to flushByteSize.
    conf.set(HStore.MEMSTORE_CLASS_NAME, MyCompactingMemStore5.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushByteSize * 200));

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    final MyCompactingMemStore5 myCompactingMemStore = ((MyCompactingMemStore5) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == flushByteSize);

    store.add(smallCell, new NonThreadSafeMemStoreSizing());
    store.add(largeCell, new NonThreadSafeMemStoreSizing());

    final AtomicReference<Throwable> exceptionRef = new AtomicReference<Throwable>();
    final Cell writeAgainCell1 = createCell(qf3, timestamp, seqId + 1, largeValue);
    final Cell writeAgainCell2 = createCell(qf4, timestamp, seqId + 1, largeValue);
    final int writeAgainCellByteSize =
      MutableSegment.getCellLength(writeAgainCell1) + MutableSegment.getCellLength(writeAgainCell2);
    final Thread writeAgainThread = new Thread(() -> {
      try {
        myCompactingMemStore.writeMemStoreAgainStartCyclicBarrier.await();

        store.add(writeAgainCell1, new NonThreadSafeMemStoreSizing());
        store.add(writeAgainCell2, new NonThreadSafeMemStoreSizing());

        myCompactingMemStore.writeMemStoreAgainEndCyclicBarrier.await();
      } catch (Throwable exception) {
        exceptionRef.set(exception);
      }
    });
    writeAgainThread.setName(MyCompactingMemStore5.WRITE_AGAIN_THREAD_NAME);
    writeAgainThread.start();

    String oldThreadName = Thread.currentThread().getName();
    try {
      Thread.currentThread().setName(MyCompactingMemStore5.TAKE_SNAPSHOT_THREAD_NAME);
      /**
       * {@link CompactingMemStore#snapshot} must wait the in memory compact thread enters
       * {@link CompactingMemStore#flattenOneSegment},because {@link CompactingMemStore#snapshot}
       * would invoke {@link CompactingMemStore#stopCompaction}.
       */
      myCompactingMemStore.snapShotStartCyclicCyclicBarrier.await();
      MemStoreSnapshot memStoreSnapshot = myCompactingMemStore.snapshot();
      myCompactingMemStore.inMemoryCompactionEndCyclicBarrier.await();
      writeAgainThread.join();

      assertTrue(memStoreSnapshot.getCellsCount() == 2);
      assertTrue(((int) (memStoreSnapshot.getDataSize())) == firstWriteCellByteSize);
      VersionedSegmentsList segments = myCompactingMemStore.getImmutableSegments();
      assertTrue(segments.getNumOfSegments() == 1);
      assertTrue(
        ((int) (segments.getStoreSegments().get(0).getDataSize())) == writeAgainCellByteSize);
      assertTrue(segments.getNumOfCells() == 2);
      assertTrue(myCompactingMemStore.setInMemoryCompactionFlagCounter.get() == 2);
      assertTrue(exceptionRef.get() == null);
      assertTrue(myCompactingMemStore.swapPipelineWithNullCounter.get() == 2);
    } finally {
      Thread.currentThread().setName(oldThreadName);
    }
  }

  /**
   * <pre>
   * This test is for HBASE-26465,
   * test {@link DefaultMemStore#clearSnapshot} and {@link DefaultMemStore#getScanners} execute
   * concurrently. The threads sequence before HBASE-26465 is:
   * 1.The flush thread starts {@link DefaultMemStore} flushing after some cells have be added to
   *  {@link DefaultMemStore}.
   * 2.The flush thread stopping before {@link DefaultMemStore#clearSnapshot} in
   *   {@link HStore#updateStorefiles} after completed flushing memStore to hfile.
   * 3.The scan thread starts and stopping after {@link DefaultMemStore#getSnapshotSegments} in
   *   {@link DefaultMemStore#getScanners},here the scan thread gets the
   *   {@link DefaultMemStore#snapshot} which is created by the flush thread.
   * 4.The flush thread continues {@link DefaultMemStore#clearSnapshot} and close
   *   {@link DefaultMemStore#snapshot},because the reference count of the corresponding
   *   {@link MemStoreLABImpl} is 0, the {@link Chunk}s in corresponding {@link MemStoreLABImpl}
   *   are recycled.
   * 5.The scan thread continues {@link DefaultMemStore#getScanners},and create a
   *   {@link SegmentScanner} for this {@link DefaultMemStore#snapshot}, and increase the
   *   reference count of the corresponding {@link MemStoreLABImpl}, but {@link Chunk}s in
   *   corresponding {@link MemStoreLABImpl} are recycled by step 4, and these {@link Chunk}s may
   *   be overwritten by other write threads,which may cause serious problem.
   * After HBASE-26465,{@link DefaultMemStore#getScanners} and
   * {@link DefaultMemStore#clearSnapshot} could not execute concurrently.
   * </pre>
   */
  @Test
  public void testClearSnapshotGetScannerConcurrently() throws Exception {
    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);

    conf.set(HStore.MEMSTORE_CLASS_NAME, MyDefaultMemStore.class.getName());
    conf.setBoolean(WALFactory.WAL_ENABLED, false);

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family).build());
    MyDefaultMemStore myDefaultMemStore = (MyDefaultMemStore) (store.memstore);
    myDefaultMemStore.store = store;

    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    store.add(smallCell, memStoreSizing);
    store.add(largeCell, memStoreSizing);

    final AtomicReference<Throwable> exceptionRef = new AtomicReference<Throwable>();
    final Thread flushThread = new Thread(() -> {
      try {
        flushStore(store, id++);
      } catch (Throwable exception) {
        exceptionRef.set(exception);
      }
    });
    flushThread.setName(MyDefaultMemStore.FLUSH_THREAD_NAME);
    flushThread.start();

    String oldThreadName = Thread.currentThread().getName();
    StoreScanner storeScanner = null;
    try {
      Thread.currentThread().setName(MyDefaultMemStore.GET_SCANNER_THREAD_NAME);

      /**
       * Wait flush thread stopping before {@link DefaultMemStore#doClearSnapshot}
       */
      myDefaultMemStore.getScannerCyclicBarrier.await();

      storeScanner = (StoreScanner) store.getScanner(new Scan(new Get(row)), quals, seqId + 1);
      flushThread.join();

      if (myDefaultMemStore.shouldWait) {
        SegmentScanner segmentScanner = getTypeKeyValueScanner(storeScanner, SegmentScanner.class);
        MemStoreLABImpl memStoreLAB = (MemStoreLABImpl) (segmentScanner.segment.getMemStoreLAB());
        assertTrue(memStoreLAB.isClosed());
        assertTrue(!memStoreLAB.chunks.isEmpty());
        assertTrue(!memStoreLAB.isReclaimed());

        Cell cell1 = segmentScanner.next();
        CellUtil.equals(smallCell, cell1);
        Cell cell2 = segmentScanner.next();
        CellUtil.equals(largeCell, cell2);
        assertNull(segmentScanner.next());
      } else {
        List<Cell> results = new ArrayList<>();
        storeScanner.next(results);
        assertEquals(2, results.size());
        CellUtil.equals(smallCell, results.get(0));
        CellUtil.equals(largeCell, results.get(1));
      }
      assertTrue(exceptionRef.get() == null);
    } finally {
      if (storeScanner != null) {
        storeScanner.close();
      }
      Thread.currentThread().setName(oldThreadName);
    }
  }

  @SuppressWarnings("unchecked")
  private <T> T getTypeKeyValueScanner(StoreScanner storeScanner, Class<T> keyValueScannerClass) {
    List<T> resultScanners = new ArrayList<T>();
    for (KeyValueScanner keyValueScanner : storeScanner.currentScanners) {
      if (keyValueScannerClass.isInstance(keyValueScanner)) {
        resultScanners.add((T) keyValueScanner);
      }
    }
    assertTrue(resultScanners.size() == 1);
    return resultScanners.get(0);
  }

  @Test
  public void testOnConfigurationChange() throws IOException {
    final int COMMON_MAX_FILES_TO_COMPACT = 10;
    final int NEW_COMMON_MAX_FILES_TO_COMPACT = 8;
    final int STORE_MAX_FILES_TO_COMPACT = 6;

    // Build a table that its maxFileToCompact different from common configuration.
    Configuration conf = HBaseConfiguration.create();
    conf.setInt(CompactionConfiguration.HBASE_HSTORE_COMPACTION_MAX_KEY,
      COMMON_MAX_FILES_TO_COMPACT);
    conf.setBoolean(CACHE_DATA_ON_READ_KEY, false);
    conf.setBoolean(CACHE_BLOCKS_ON_WRITE_KEY, true);
    conf.setBoolean(EVICT_BLOCKS_ON_CLOSE_KEY, true);
    ColumnFamilyDescriptor hcd = ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setConfiguration(CompactionConfiguration.HBASE_HSTORE_COMPACTION_MAX_KEY,
        String.valueOf(STORE_MAX_FILES_TO_COMPACT))
      .build();
    init(this.name.getMethodName(), conf, hcd);

    // After updating common configuration, the conf in HStore itself must not be changed.
    conf.setInt(CompactionConfiguration.HBASE_HSTORE_COMPACTION_MAX_KEY,
      NEW_COMMON_MAX_FILES_TO_COMPACT);
    this.store.onConfigurationChange(conf);

    assertEquals(STORE_MAX_FILES_TO_COMPACT,
      store.getStoreEngine().getCompactionPolicy().getConf().getMaxFilesToCompact());

    assertEquals(conf.getBoolean(CACHE_DATA_ON_READ_KEY, DEFAULT_CACHE_DATA_ON_READ), false);
    assertEquals(conf.getBoolean(CACHE_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_DATA_ON_WRITE), true);
    assertEquals(conf.getBoolean(EVICT_BLOCKS_ON_CLOSE_KEY, DEFAULT_EVICT_ON_CLOSE), true);

    // reset to default values
    conf.getBoolean(CACHE_DATA_ON_READ_KEY, DEFAULT_CACHE_DATA_ON_READ);
    conf.getBoolean(CACHE_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_DATA_ON_WRITE);
    conf.getBoolean(EVICT_BLOCKS_ON_CLOSE_KEY, DEFAULT_EVICT_ON_CLOSE);
    this.store.onConfigurationChange(conf);
  }

  /**
   * This test is for HBASE-26476
   */
  @Test
  public void testExtendsDefaultMemStore() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    conf.setBoolean(WALFactory.WAL_ENABLED, false);

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family).build());
    assertTrue(this.store.memstore.getClass() == DefaultMemStore.class);
    tearDown();

    conf.set(HStore.MEMSTORE_CLASS_NAME, CustomDefaultMemStore.class.getName());
    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family).build());
    assertTrue(this.store.memstore.getClass() == CustomDefaultMemStore.class);
  }

  static class CustomDefaultMemStore extends DefaultMemStore {

    public CustomDefaultMemStore(Configuration conf, CellComparator c,
      RegionServicesForStores regionServices) {
      super(conf, c, regionServices);
    }

  }

  /**
   * This test is for HBASE-26488
   */
  @Test
  public void testMemoryLeakWhenFlushMemStoreRetrying() throws Exception {

    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell = createCell(qf2, timestamp, seqId, largeValue);
    TreeSet<byte[]> quals = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    quals.add(qf1);
    quals.add(qf2);

    conf.set(HStore.MEMSTORE_CLASS_NAME, MyDefaultMemStore1.class.getName());
    conf.setBoolean(WALFactory.WAL_ENABLED, false);
    conf.set(DefaultStoreEngine.DEFAULT_STORE_FLUSHER_CLASS_KEY,
      MyDefaultStoreFlusher.class.getName());

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family).build());
    MyDefaultMemStore1 myDefaultMemStore = (MyDefaultMemStore1) (store.memstore);
    assertTrue((store.storeEngine.getStoreFlusher()) instanceof MyDefaultStoreFlusher);

    MemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    store.add(smallCell, memStoreSizing);
    store.add(largeCell, memStoreSizing);
    flushStore(store, id++);

    MemStoreLABImpl memStoreLAB =
      (MemStoreLABImpl) (myDefaultMemStore.snapshotImmutableSegment.getMemStoreLAB());
    assertTrue(memStoreLAB.isClosed());
    assertTrue(memStoreLAB.getRefCntValue() == 0);
    assertTrue(memStoreLAB.isReclaimed());
    assertTrue(memStoreLAB.chunks.isEmpty());
    StoreScanner storeScanner = null;
    try {
      storeScanner = (StoreScanner) store.getScanner(new Scan(new Get(row)), quals, seqId + 1);
      assertTrue(store.storeEngine.getStoreFileManager().getStorefileCount() == 1);
      assertTrue(store.memstore.size().getCellsCount() == 0);
      assertTrue(store.memstore.getSnapshotSize().getCellsCount() == 0);
      assertTrue(storeScanner.currentScanners.size() == 1);
      assertTrue(storeScanner.currentScanners.get(0) instanceof StoreFileScanner);

      List<Cell> results = new ArrayList<>();
      storeScanner.next(results);
      assertEquals(2, results.size());
      CellUtil.equals(smallCell, results.get(0));
      CellUtil.equals(largeCell, results.get(1));
    } finally {
      if (storeScanner != null) {
        storeScanner.close();
      }
    }
  }

  static class MyDefaultMemStore1 extends DefaultMemStore {

    private ImmutableSegment snapshotImmutableSegment;

    public MyDefaultMemStore1(Configuration conf, CellComparator c,
      RegionServicesForStores regionServices) {
      super(conf, c, regionServices);
    }

    @Override
    public MemStoreSnapshot snapshot() {
      MemStoreSnapshot result = super.snapshot();
      this.snapshotImmutableSegment = snapshot;
      return result;
    }

  }

  public static class MyDefaultStoreFlusher extends DefaultStoreFlusher {
    private static final AtomicInteger failCounter = new AtomicInteger(1);
    private static final AtomicInteger counter = new AtomicInteger(0);

    public MyDefaultStoreFlusher(Configuration conf, HStore store) {
      super(conf, store);
    }

    @Override
    public List<Path> flushSnapshot(MemStoreSnapshot snapshot, long cacheFlushId,
      MonitoredTask status, ThroughputController throughputController,
      FlushLifeCycleTracker tracker, Consumer<Path> writerCreationTracker) throws IOException {
      counter.incrementAndGet();
      return super.flushSnapshot(snapshot, cacheFlushId, status, throughputController, tracker,
        writerCreationTracker);
    }

    @Override
    protected void performFlush(InternalScanner scanner, final CellSink sink,
      ThroughputController throughputController) throws IOException {

      final int currentCount = counter.get();
      CellSink newCellSink = (cell) -> {
        if (currentCount <= failCounter.get()) {
          throw new IOException("Simulated exception by tests");
        }
        sink.append(cell);
      };
      super.performFlush(scanner, newCellSink, throughputController);
    }
  }

  /**
   * This test is for HBASE-26494, test the {@link RefCnt} behaviors in {@link ImmutableMemStoreLAB}
   */
  @Test
  public void testImmutableMemStoreLABRefCnt() throws Exception {
    Configuration conf = HBaseConfiguration.create();

    byte[] smallValue = new byte[3];
    byte[] largeValue = new byte[9];
    final long timestamp = EnvironmentEdgeManager.currentTime();
    final long seqId = 100;
    final Cell smallCell1 = createCell(qf1, timestamp, seqId, smallValue);
    final Cell largeCell1 = createCell(qf2, timestamp, seqId, largeValue);
    final Cell smallCell2 = createCell(qf3, timestamp, seqId + 1, smallValue);
    final Cell largeCell2 = createCell(qf4, timestamp, seqId + 1, largeValue);
    final Cell smallCell3 = createCell(qf5, timestamp, seqId + 2, smallValue);
    final Cell largeCell3 = createCell(qf6, timestamp, seqId + 2, largeValue);

    int smallCellByteSize = MutableSegment.getCellLength(smallCell1);
    int largeCellByteSize = MutableSegment.getCellLength(largeCell1);
    int firstWriteCellByteSize = (smallCellByteSize + largeCellByteSize);
    int flushByteSize = firstWriteCellByteSize - 2;

    // set CompactingMemStore.inmemoryFlushSize to flushByteSize.
    conf.set(HStore.MEMSTORE_CLASS_NAME, CompactingMemStore.class.getName());
    conf.setDouble(CompactingMemStore.IN_MEMORY_FLUSH_THRESHOLD_FACTOR_KEY, 0.005);
    conf.set(HConstants.HREGION_MEMSTORE_FLUSH_SIZE, String.valueOf(flushByteSize * 200));
    conf.setBoolean(WALFactory.WAL_ENABLED, false);

    init(name.getMethodName(), conf, ColumnFamilyDescriptorBuilder.newBuilder(family)
      .setInMemoryCompaction(MemoryCompactionPolicy.BASIC).build());

    final CompactingMemStore myCompactingMemStore = ((CompactingMemStore) store.memstore);
    assertTrue((int) (myCompactingMemStore.getInmemoryFlushSize()) == flushByteSize);
    myCompactingMemStore.allowCompaction.set(false);

    NonThreadSafeMemStoreSizing memStoreSizing = new NonThreadSafeMemStoreSizing();
    store.add(smallCell1, memStoreSizing);
    store.add(largeCell1, memStoreSizing);
    store.add(smallCell2, memStoreSizing);
    store.add(largeCell2, memStoreSizing);
    store.add(smallCell3, memStoreSizing);
    store.add(largeCell3, memStoreSizing);
    VersionedSegmentsList versionedSegmentsList = myCompactingMemStore.getImmutableSegments();
    assertTrue(versionedSegmentsList.getNumOfSegments() == 3);
    List<ImmutableSegment> segments = versionedSegmentsList.getStoreSegments();
    List<MemStoreLABImpl> memStoreLABs = new ArrayList<MemStoreLABImpl>(segments.size());
    for (ImmutableSegment segment : segments) {
      memStoreLABs.add((MemStoreLABImpl) segment.getMemStoreLAB());
    }
    List<KeyValueScanner> scanners1 = myCompactingMemStore.getScanners(Long.MAX_VALUE);
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 2);
    }

    myCompactingMemStore.allowCompaction.set(true);
    myCompactingMemStore.flushInMemory();

    versionedSegmentsList = myCompactingMemStore.getImmutableSegments();
    assertTrue(versionedSegmentsList.getNumOfSegments() == 1);
    ImmutableMemStoreLAB immutableMemStoreLAB =
      (ImmutableMemStoreLAB) (versionedSegmentsList.getStoreSegments().get(0).getMemStoreLAB());
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 2);
    }

    List<KeyValueScanner> scanners2 = myCompactingMemStore.getScanners(Long.MAX_VALUE);
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 2);
    }
    assertTrue(immutableMemStoreLAB.getRefCntValue() == 2);
    for (KeyValueScanner scanner : scanners1) {
      scanner.close();
    }
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 1);
    }
    for (KeyValueScanner scanner : scanners2) {
      scanner.close();
    }
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 1);
    }
    assertTrue(immutableMemStoreLAB.getRefCntValue() == 1);
    flushStore(store, id++);
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.getRefCntValue() == 0);
    }
    assertTrue(immutableMemStoreLAB.getRefCntValue() == 0);
    assertTrue(immutableMemStoreLAB.isClosed());
    for (MemStoreLABImpl memStoreLAB : memStoreLABs) {
      assertTrue(memStoreLAB.isClosed());
      assertTrue(memStoreLAB.isReclaimed());
      assertTrue(memStoreLAB.chunks.isEmpty());
    }
  }

  private HStoreFile mockStoreFileWithLength(long length) {
    HStoreFile sf = mock(HStoreFile.class);
    StoreFileReader sfr = mock(StoreFileReader.class);
    when(sf.isHFile()).thenReturn(true);
    when(sf.getReader()).thenReturn(sfr);
    when(sfr.length()).thenReturn(length);
    return sf;
  }

  private static class MyThread extends Thread {
    private StoreScanner scanner;
    private KeyValueHeap heap;

    public MyThread(StoreScanner scanner) {
      this.scanner = scanner;
    }

    public KeyValueHeap getHeap() {
      return this.heap;
    }

    @Override
    public void run() {
      scanner.trySwitchToStreamRead();
      heap = scanner.heap;
    }
  }

  private static class MyMemStoreCompactor extends MemStoreCompactor {
    private static final AtomicInteger RUNNER_COUNT = new AtomicInteger(0);
    private static final CountDownLatch START_COMPACTOR_LATCH = new CountDownLatch(1);

    public MyMemStoreCompactor(CompactingMemStore compactingMemStore,
      MemoryCompactionPolicy compactionPolicy) throws IllegalArgumentIOException {
      super(compactingMemStore, compactionPolicy);
    }

    @Override
    public boolean start() throws IOException {
      boolean isFirst = RUNNER_COUNT.getAndIncrement() == 0;
      if (isFirst) {
        try {
          START_COMPACTOR_LATCH.await();
          return super.start();
        } catch (InterruptedException ex) {
          throw new RuntimeException(ex);
        }
      }
      return super.start();
    }
  }

  public static class MyCompactingMemStoreWithCustomCompactor extends CompactingMemStore {
    private static final AtomicInteger RUNNER_COUNT = new AtomicInteger(0);

    public MyCompactingMemStoreWithCustomCompactor(Configuration conf, CellComparatorImpl c,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, c, store, regionServices, compactionPolicy);
    }

    @Override
    protected MemStoreCompactor createMemStoreCompactor(MemoryCompactionPolicy compactionPolicy)
      throws IllegalArgumentIOException {
      return new MyMemStoreCompactor(this, compactionPolicy);
    }

    @Override
    protected boolean setInMemoryCompactionFlag() {
      boolean rval = super.setInMemoryCompactionFlag();
      if (rval) {
        RUNNER_COUNT.incrementAndGet();
        if (LOG.isDebugEnabled()) {
          LOG.debug("runner count: " + RUNNER_COUNT.get());
        }
      }
      return rval;
    }
  }

  public static class MyCompactingMemStore extends CompactingMemStore {
    private static final AtomicBoolean START_TEST = new AtomicBoolean(false);
    private final CountDownLatch getScannerLatch = new CountDownLatch(1);
    private final CountDownLatch snapshotLatch = new CountDownLatch(1);

    public MyCompactingMemStore(Configuration conf, CellComparatorImpl c, HStore store,
      RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, c, store, regionServices, compactionPolicy);
    }

    @Override
    protected List<KeyValueScanner> createList(int capacity) {
      if (START_TEST.get()) {
        try {
          getScannerLatch.countDown();
          snapshotLatch.await();
        } catch (InterruptedException e) {
          throw new RuntimeException(e);
        }
      }
      return new ArrayList<>(capacity);
    }

    @Override
    protected void pushActiveToPipeline(MutableSegment active, boolean checkEmpty) {
      if (START_TEST.get()) {
        try {
          getScannerLatch.await();
        } catch (InterruptedException e) {
          throw new RuntimeException(e);
        }
      }

      super.pushActiveToPipeline(active, checkEmpty);
      if (START_TEST.get()) {
        snapshotLatch.countDown();
      }
    }
  }

  interface MyListHook {
    void hook(int currentSize);
  }

  private static class MyList<T> implements List<T> {
    private final List<T> delegatee = new ArrayList<>();
    private final MyListHook hookAtAdd;

    MyList(final MyListHook hookAtAdd) {
      this.hookAtAdd = hookAtAdd;
    }

    @Override
    public int size() {
      return delegatee.size();
    }

    @Override
    public boolean isEmpty() {
      return delegatee.isEmpty();
    }

    @Override
    public boolean contains(Object o) {
      return delegatee.contains(o);
    }

    @Override
    public Iterator<T> iterator() {
      return delegatee.iterator();
    }

    @Override
    public Object[] toArray() {
      return delegatee.toArray();
    }

    @Override
    public <R> R[] toArray(R[] a) {
      return delegatee.toArray(a);
    }

    @Override
    public boolean add(T e) {
      hookAtAdd.hook(size());
      return delegatee.add(e);
    }

    @Override
    public boolean remove(Object o) {
      return delegatee.remove(o);
    }

    @Override
    public boolean containsAll(Collection<?> c) {
      return delegatee.containsAll(c);
    }

    @Override
    public boolean addAll(Collection<? extends T> c) {
      return delegatee.addAll(c);
    }

    @Override
    public boolean addAll(int index, Collection<? extends T> c) {
      return delegatee.addAll(index, c);
    }

    @Override
    public boolean removeAll(Collection<?> c) {
      return delegatee.removeAll(c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      return delegatee.retainAll(c);
    }

    @Override
    public void clear() {
      delegatee.clear();
    }

    @Override
    public T get(int index) {
      return delegatee.get(index);
    }

    @Override
    public T set(int index, T element) {
      return delegatee.set(index, element);
    }

    @Override
    public void add(int index, T element) {
      delegatee.add(index, element);
    }

    @Override
    public T remove(int index) {
      return delegatee.remove(index);
    }

    @Override
    public int indexOf(Object o) {
      return delegatee.indexOf(o);
    }

    @Override
    public int lastIndexOf(Object o) {
      return delegatee.lastIndexOf(o);
    }

    @Override
    public ListIterator<T> listIterator() {
      return delegatee.listIterator();
    }

    @Override
    public ListIterator<T> listIterator(int index) {
      return delegatee.listIterator(index);
    }

    @Override
    public List<T> subList(int fromIndex, int toIndex) {
      return delegatee.subList(fromIndex, toIndex);
    }
  }

  public static class MyCompactingMemStore2 extends CompactingMemStore {
    private static final String LARGE_CELL_THREAD_NAME = "largeCellThread";
    private static final String SMALL_CELL_THREAD_NAME = "smallCellThread";
    private final CyclicBarrier preCyclicBarrier = new CyclicBarrier(2);
    private final CyclicBarrier postCyclicBarrier = new CyclicBarrier(2);
    private final AtomicInteger largeCellPreUpdateCounter = new AtomicInteger(0);
    private final AtomicInteger smallCellPreUpdateCounter = new AtomicInteger(0);

    public MyCompactingMemStore2(Configuration conf, CellComparatorImpl cellComparator,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, cellComparator, store, regionServices, compactionPolicy);
    }

    @Override
    protected boolean checkAndAddToActiveSize(MutableSegment currActive, Cell cellToAdd,
      MemStoreSizing memstoreSizing) {
      if (Thread.currentThread().getName().equals(LARGE_CELL_THREAD_NAME)) {
        int currentCount = largeCellPreUpdateCounter.incrementAndGet();
        if (currentCount <= 1) {
          try {
            /**
             * smallCellThread enters CompactingMemStore.checkAndAddToActiveSize first, then
             * largeCellThread enters CompactingMemStore.checkAndAddToActiveSize, and then
             * largeCellThread invokes flushInMemory.
             */
            preCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }
      }

      boolean returnValue = super.checkAndAddToActiveSize(currActive, cellToAdd, memstoreSizing);
      if (Thread.currentThread().getName().equals(SMALL_CELL_THREAD_NAME)) {
        try {
          preCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
      return returnValue;
    }

    @Override
    protected void doAdd(MutableSegment currentActive, Cell cell, MemStoreSizing memstoreSizing) {
      if (Thread.currentThread().getName().equals(SMALL_CELL_THREAD_NAME)) {
        try {
          /**
           * After largeCellThread finished flushInMemory method, smallCellThread can add cell to
           * currentActive . That is to say when largeCellThread called flushInMemory method,
           * currentActive has no cell.
           */
          postCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
      super.doAdd(currentActive, cell, memstoreSizing);
    }

    @Override
    protected void flushInMemory(MutableSegment currentActiveMutableSegment) {
      super.flushInMemory(currentActiveMutableSegment);
      if (Thread.currentThread().getName().equals(LARGE_CELL_THREAD_NAME)) {
        if (largeCellPreUpdateCounter.get() <= 1) {
          try {
            postCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }
      }
    }

  }

  public static class MyCompactingMemStore3 extends CompactingMemStore {
    private static final String LARGE_CELL_THREAD_NAME = "largeCellThread";
    private static final String SMALL_CELL_THREAD_NAME = "smallCellThread";

    private final CyclicBarrier preCyclicBarrier = new CyclicBarrier(2);
    private final CyclicBarrier postCyclicBarrier = new CyclicBarrier(2);
    private final AtomicInteger flushCounter = new AtomicInteger(0);
    private static final int CELL_COUNT = 5;
    private boolean flushByteSizeLessThanSmallAndLargeCellSize = true;

    public MyCompactingMemStore3(Configuration conf, CellComparatorImpl cellComparator,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, cellComparator, store, regionServices, compactionPolicy);
    }

    @Override
    protected boolean checkAndAddToActiveSize(MutableSegment currActive, Cell cellToAdd,
      MemStoreSizing memstoreSizing) {
      if (!flushByteSizeLessThanSmallAndLargeCellSize) {
        return super.checkAndAddToActiveSize(currActive, cellToAdd, memstoreSizing);
      }
      if (Thread.currentThread().getName().equals(LARGE_CELL_THREAD_NAME)) {
        try {
          preCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }

      boolean returnValue = super.checkAndAddToActiveSize(currActive, cellToAdd, memstoreSizing);
      if (Thread.currentThread().getName().equals(SMALL_CELL_THREAD_NAME)) {
        try {
          preCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
      return returnValue;
    }

    @Override
    protected void postUpdate(MutableSegment currentActiveMutableSegment) {
      super.postUpdate(currentActiveMutableSegment);
      if (!flushByteSizeLessThanSmallAndLargeCellSize) {
        try {
          postCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
        return;
      }

      if (Thread.currentThread().getName().equals(SMALL_CELL_THREAD_NAME)) {
        try {
          postCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
    }

    @Override
    protected void flushInMemory(MutableSegment currentActiveMutableSegment) {
      super.flushInMemory(currentActiveMutableSegment);
      flushCounter.incrementAndGet();
      if (!flushByteSizeLessThanSmallAndLargeCellSize) {
        return;
      }

      assertTrue(Thread.currentThread().getName().equals(LARGE_CELL_THREAD_NAME));
      try {
        postCyclicBarrier.await();
      } catch (Throwable e) {
        throw new RuntimeException(e);
      }

    }

    void disableCompaction() {
      allowCompaction.set(false);
    }

    void enableCompaction() {
      allowCompaction.set(true);
    }

  }

  public static class MyCompactingMemStore4 extends CompactingMemStore {
    private static final String TAKE_SNAPSHOT_THREAD_NAME = "takeSnapShotThread";
    /**
     * {@link CompactingMemStore#flattenOneSegment} must execute after
     * {@link CompactingMemStore#getImmutableSegments}
     */
    private final CyclicBarrier flattenOneSegmentPreCyclicBarrier = new CyclicBarrier(2);
    /**
     * Only after {@link CompactingMemStore#flattenOneSegment} completed,
     * {@link CompactingMemStore#swapPipelineWithNull} could execute.
     */
    private final CyclicBarrier flattenOneSegmentPostCyclicBarrier = new CyclicBarrier(2);
    /**
     * Only the in memory compact thread enters {@link CompactingMemStore#flattenOneSegment},the
     * snapshot thread starts {@link CompactingMemStore#snapshot},because
     * {@link CompactingMemStore#snapshot} would invoke {@link CompactingMemStore#stopCompaction}.
     */
    private final CyclicBarrier snapShotStartCyclicCyclicBarrier = new CyclicBarrier(2);
    /**
     * To wait for {@link CompactingMemStore.InMemoryCompactionRunnable} stopping.
     */
    private final CyclicBarrier inMemoryCompactionEndCyclicBarrier = new CyclicBarrier(2);
    private final AtomicInteger getImmutableSegmentsListCounter = new AtomicInteger(0);
    private final AtomicInteger swapPipelineWithNullCounter = new AtomicInteger(0);
    private final AtomicInteger flattenOneSegmentCounter = new AtomicInteger(0);
    private final AtomicInteger setInMemoryCompactionFlagCounter = new AtomicInteger(0);

    public MyCompactingMemStore4(Configuration conf, CellComparatorImpl cellComparator,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, cellComparator, store, regionServices, compactionPolicy);
    }

    @Override
    public VersionedSegmentsList getImmutableSegments() {
      VersionedSegmentsList result = super.getImmutableSegments();
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = getImmutableSegmentsListCounter.incrementAndGet();
        if (currentCount <= 1) {
          try {
            flattenOneSegmentPreCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }
      }
      return result;
    }

    @Override
    protected boolean swapPipelineWithNull(VersionedSegmentsList segments) {
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = swapPipelineWithNullCounter.incrementAndGet();
        if (currentCount <= 1) {
          try {
            flattenOneSegmentPostCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }
      }
      boolean result = super.swapPipelineWithNull(segments);
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = swapPipelineWithNullCounter.get();
        if (currentCount <= 1) {
          assertTrue(!result);
        }
        if (currentCount == 2) {
          assertTrue(result);
        }
      }
      return result;

    }

    @Override
    public void flattenOneSegment(long requesterVersion, Action action) {
      int currentCount = flattenOneSegmentCounter.incrementAndGet();
      if (currentCount <= 1) {
        try {
          /**
           * {@link CompactingMemStore#snapshot} could start.
           */
          snapShotStartCyclicCyclicBarrier.await();
          flattenOneSegmentPreCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
      super.flattenOneSegment(requesterVersion, action);
      if (currentCount <= 1) {
        try {
          flattenOneSegmentPostCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
    }

    @Override
    protected boolean setInMemoryCompactionFlag() {
      boolean result = super.setInMemoryCompactionFlag();
      assertTrue(result);
      setInMemoryCompactionFlagCounter.incrementAndGet();
      return result;
    }

    @Override
    void inMemoryCompaction() {
      try {
        super.inMemoryCompaction();
      } finally {
        try {
          inMemoryCompactionEndCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }

      }
    }

  }

  public static class MyCompactingMemStore5 extends CompactingMemStore {
    private static final String TAKE_SNAPSHOT_THREAD_NAME = "takeSnapShotThread";
    private static final String WRITE_AGAIN_THREAD_NAME = "writeAgainThread";
    /**
     * {@link CompactingMemStore#flattenOneSegment} must execute after
     * {@link CompactingMemStore#getImmutableSegments}
     */
    private final CyclicBarrier flattenOneSegmentPreCyclicBarrier = new CyclicBarrier(2);
    /**
     * Only after {@link CompactingMemStore#flattenOneSegment} completed,
     * {@link CompactingMemStore#swapPipelineWithNull} could execute.
     */
    private final CyclicBarrier flattenOneSegmentPostCyclicBarrier = new CyclicBarrier(2);
    /**
     * Only the in memory compact thread enters {@link CompactingMemStore#flattenOneSegment},the
     * snapshot thread starts {@link CompactingMemStore#snapshot},because
     * {@link CompactingMemStore#snapshot} would invoke {@link CompactingMemStore#stopCompaction}.
     */
    private final CyclicBarrier snapShotStartCyclicCyclicBarrier = new CyclicBarrier(2);
    /**
     * To wait for {@link CompactingMemStore.InMemoryCompactionRunnable} stopping.
     */
    private final CyclicBarrier inMemoryCompactionEndCyclicBarrier = new CyclicBarrier(2);
    private final AtomicInteger getImmutableSegmentsListCounter = new AtomicInteger(0);
    private final AtomicInteger swapPipelineWithNullCounter = new AtomicInteger(0);
    private final AtomicInteger flattenOneSegmentCounter = new AtomicInteger(0);
    private final AtomicInteger setInMemoryCompactionFlagCounter = new AtomicInteger(0);
    /**
     * Only the snapshot thread retry {@link CompactingMemStore#swapPipelineWithNull}, writeAgain
     * thread could start.
     */
    private final CyclicBarrier writeMemStoreAgainStartCyclicBarrier = new CyclicBarrier(2);
    /**
     * This is used for snapshot thread,writeAgain thread and in memory compact thread. Only the
     * writeAgain thread completes, {@link CompactingMemStore#swapPipelineWithNull} would
     * execute,and in memory compact thread would exit,because we expect that in memory compact
     * executing only once.
     */
    private final CyclicBarrier writeMemStoreAgainEndCyclicBarrier = new CyclicBarrier(3);

    public MyCompactingMemStore5(Configuration conf, CellComparatorImpl cellComparator,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, cellComparator, store, regionServices, compactionPolicy);
    }

    @Override
    public VersionedSegmentsList getImmutableSegments() {
      VersionedSegmentsList result = super.getImmutableSegments();
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = getImmutableSegmentsListCounter.incrementAndGet();
        if (currentCount <= 1) {
          try {
            flattenOneSegmentPreCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }

      }

      return result;
    }

    @Override
    protected boolean swapPipelineWithNull(VersionedSegmentsList segments) {
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = swapPipelineWithNullCounter.incrementAndGet();
        if (currentCount <= 1) {
          try {
            flattenOneSegmentPostCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }

        if (currentCount == 2) {
          try {
            /**
             * Only the snapshot thread retry {@link CompactingMemStore#swapPipelineWithNull},
             * writeAgain thread could start.
             */
            writeMemStoreAgainStartCyclicBarrier.await();
            /**
             * Only the writeAgain thread completes, retry
             * {@link CompactingMemStore#swapPipelineWithNull} would execute.
             */
            writeMemStoreAgainEndCyclicBarrier.await();
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }

      }
      boolean result = super.swapPipelineWithNull(segments);
      if (Thread.currentThread().getName().equals(TAKE_SNAPSHOT_THREAD_NAME)) {
        int currentCount = swapPipelineWithNullCounter.get();
        if (currentCount <= 1) {
          assertTrue(!result);
        }
        if (currentCount == 2) {
          assertTrue(result);
        }
      }
      return result;

    }

    @Override
    public void flattenOneSegment(long requesterVersion, Action action) {
      int currentCount = flattenOneSegmentCounter.incrementAndGet();
      if (currentCount <= 1) {
        try {
          /**
           * {@link CompactingMemStore#snapshot} could start.
           */
          snapShotStartCyclicCyclicBarrier.await();
          flattenOneSegmentPreCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }
      }
      super.flattenOneSegment(requesterVersion, action);
      if (currentCount <= 1) {
        try {
          flattenOneSegmentPostCyclicBarrier.await();
          /**
           * Only the writeAgain thread completes, in memory compact thread would exit,because we
           * expect that in memory compact executing only once.
           */
          writeMemStoreAgainEndCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }

      }
    }

    @Override
    protected boolean setInMemoryCompactionFlag() {
      boolean result = super.setInMemoryCompactionFlag();
      int count = setInMemoryCompactionFlagCounter.incrementAndGet();
      if (count <= 1) {
        assertTrue(result);
      }
      if (count == 2) {
        assertTrue(!result);
      }
      return result;
    }

    @Override
    void inMemoryCompaction() {
      try {
        super.inMemoryCompaction();
      } finally {
        try {
          inMemoryCompactionEndCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }

      }
    }
  }

  public static class MyCompactingMemStore6 extends CompactingMemStore {
    private final CyclicBarrier inMemoryCompactionEndCyclicBarrier = new CyclicBarrier(2);

    public MyCompactingMemStore6(Configuration conf, CellComparatorImpl cellComparator,
      HStore store, RegionServicesForStores regionServices, MemoryCompactionPolicy compactionPolicy)
      throws IOException {
      super(conf, cellComparator, store, regionServices, compactionPolicy);
    }

    @Override
    void inMemoryCompaction() {
      try {
        super.inMemoryCompaction();
      } finally {
        try {
          inMemoryCompactionEndCyclicBarrier.await();
        } catch (Throwable e) {
          throw new RuntimeException(e);
        }

      }
    }
  }

  public static class MyDefaultMemStore extends DefaultMemStore {
    private static final String GET_SCANNER_THREAD_NAME = "getScannerMyThread";
    private static final String FLUSH_THREAD_NAME = "flushMyThread";
    /**
     * Only when flush thread enters {@link DefaultMemStore#doClearSnapShot}, getScanner thread
     * could start.
     */
    private final CyclicBarrier getScannerCyclicBarrier = new CyclicBarrier(2);
    /**
     * Used by getScanner thread notifies flush thread {@link DefaultMemStore#getSnapshotSegments}
     * completed, {@link DefaultMemStore#doClearSnapShot} could continue.
     */
    private final CyclicBarrier preClearSnapShotCyclicBarrier = new CyclicBarrier(2);
    /**
     * Used by flush thread notifies getScanner thread {@link DefaultMemStore#doClearSnapShot}
     * completed, {@link DefaultMemStore#getScanners} could continue.
     */
    private final CyclicBarrier postClearSnapShotCyclicBarrier = new CyclicBarrier(2);
    private final AtomicInteger getSnapshotSegmentsCounter = new AtomicInteger(0);
    private final AtomicInteger clearSnapshotCounter = new AtomicInteger(0);
    private volatile boolean shouldWait = true;
    private volatile HStore store = null;

    public MyDefaultMemStore(Configuration conf, CellComparator cellComparator,
      RegionServicesForStores regionServices) throws IOException {
      super(conf, cellComparator, regionServices);
    }

    @Override
    protected List<Segment> getSnapshotSegments() {

      List<Segment> result = super.getSnapshotSegments();

      if (Thread.currentThread().getName().equals(GET_SCANNER_THREAD_NAME)) {
        int currentCount = getSnapshotSegmentsCounter.incrementAndGet();
        if (currentCount == 1) {
          if (this.shouldWait) {
            try {
              /**
               * Notify flush thread {@link DefaultMemStore#getSnapshotSegments} completed,
               * {@link DefaultMemStore#doClearSnapShot} could continue.
               */
              preClearSnapShotCyclicBarrier.await();
              /**
               * Wait for {@link DefaultMemStore#doClearSnapShot} completed.
               */
              postClearSnapShotCyclicBarrier.await();

            } catch (Throwable e) {
              throw new RuntimeException(e);
            }
          }
        }
      }
      return result;
    }

    @Override
    protected void doClearSnapShot() {
      if (Thread.currentThread().getName().equals(FLUSH_THREAD_NAME)) {
        int currentCount = clearSnapshotCounter.incrementAndGet();
        if (currentCount == 1) {
          try {
            if (
              ((ReentrantReadWriteLock) store.getStoreEngine().getLock())
                .isWriteLockedByCurrentThread()
            ) {
              shouldWait = false;
            }
            /**
             * Only when flush thread enters {@link DefaultMemStore#doClearSnapShot}, getScanner
             * thread could start.
             */
            getScannerCyclicBarrier.await();

            if (shouldWait) {
              /**
               * Wait for {@link DefaultMemStore#getSnapshotSegments} completed.
               */
              preClearSnapShotCyclicBarrier.await();
            }
          } catch (Throwable e) {
            throw new RuntimeException(e);
          }
        }
      }
      super.doClearSnapShot();

      if (Thread.currentThread().getName().equals(FLUSH_THREAD_NAME)) {
        int currentCount = clearSnapshotCounter.get();
        if (currentCount == 1) {
          if (shouldWait) {
            try {
              /**
               * Notify getScanner thread {@link DefaultMemStore#doClearSnapShot} completed,
               * {@link DefaultMemStore#getScanners} could continue.
               */
              postClearSnapShotCyclicBarrier.await();
            } catch (Throwable e) {
              throw new RuntimeException(e);
            }
          }
        }
      }
    }
  }
}