/*
    * 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.coprocessor;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.NavigableSet;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.Coprocessor;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.client.Append;
  import org.apache.hadoop.hbase.client.Delete;
  import org.apache.hadoop.hbase.client.Durability;
  import org.apache.hadoop.hbase.client.Get;
  import org.apache.hadoop.hbase.client.Increment;
  import org.apache.hadoop.hbase.client.Mutation;
  import org.apache.hadoop.hbase.client.Put;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.filter.ByteArrayComparable;
  import org.apache.hadoop.hbase.filter.CompareFilter.CompareOp;
  import org.apache.hadoop.hbase.io.FSDataInputStreamWrapper;
  import org.apache.hadoop.hbase.io.Reference;
  import org.apache.hadoop.hbase.io.hfile.CacheConfig;
  import org.apache.hadoop.hbase.regionserver.DeleteTracker;
  import org.apache.hadoop.hbase.regionserver.Region;
  import org.apache.hadoop.hbase.regionserver.Region.Operation;
  import org.apache.hadoop.hbase.regionserver.InternalScanner;
  import org.apache.hadoop.hbase.regionserver.KeyValueScanner;
  import org.apache.hadoop.hbase.regionserver.MiniBatchOperationInProgress;
  import org.apache.hadoop.hbase.regionserver.RegionScanner;
  import org.apache.hadoop.hbase.regionserver.ScanType;
  import org.apache.hadoop.hbase.regionserver.Store;
  import org.apache.hadoop.hbase.regionserver.StoreFile;
  import org.apache.hadoop.hbase.regionserver.compactions.CompactionRequest;
  import org.apache.hadoop.hbase.regionserver.wal.HLogKey;
  import org.apache.hadoop.hbase.wal.WALKey;
  import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
  import org.apache.hadoop.hbase.util.Pair;
  
  import com.google.common.collect.ImmutableList;
  
  /**
   * Coprocessors implement this interface to observe and mediate client actions
   * on the region.
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
  @InterfaceStability.Evolving
  // TODO as method signatures need to break, update to
  // ObserverContext<? extends RegionCoprocessorEnvironment>
  // so we can use additional environment state that isn't exposed to coprocessors.
  public interface RegionObserver extends Coprocessor {
  
    /** Mutation type for postMutationBeforeWAL hook */
    public enum MutationType {
      APPEND, INCREMENT
    }
  
    /**
     * Called before the region is reported as open to the master.
     * @param c the environment provided by the region server
     * @throws IOException if an error occurred on the coprocessor
     */
    void preOpen(final ObserverContext<RegionCoprocessorEnvironment> c) throws IOException;
  
    /**
     * Called after the region is reported as open to the master.
     * @param c the environment provided by the region server
     */
    void postOpen(final ObserverContext<RegionCoprocessorEnvironment> c);
  
    /**
     * Called after the log replay on the region is over.
     * @param c the environment provided by the region server
     */
    void postLogReplay(final ObserverContext<RegionCoprocessorEnvironment> c);
 
   /**
    * Called before a memstore is flushed to disk and prior to creating the scanner to read from
    * the memstore.  To override or modify how a memstore is flushed,
    * implementing classes can return a new scanner to provide the KeyValues to be
    * stored into the new {@code StoreFile} or null to perform the default processing.
    * Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param c the environment provided by the region server
    * @param store the store being flushed
    * @param memstoreScanner the scanner for the memstore that is flushed
    * @param s the base scanner, if not {@code null}, from previous RegionObserver in the chain
    * @return the scanner to use during the flush.  {@code null} if the default implementation
    * is to be used.
    * @throws IOException if an error occurred on the coprocessor
    */
   InternalScanner preFlushScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final KeyValueScanner memstoreScanner, final InternalScanner s)
       throws IOException;
 
   /**
    * Called before the memstore is flushed to disk.
    * @param c the environment provided by the region server
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated use {@link #preFlush(ObserverContext, Store, InternalScanner)} instead
    */
   void preFlush(final ObserverContext<RegionCoprocessorEnvironment> c) throws IOException;
 
   /**
    * Called before a Store's memstore is flushed to disk.
    * @param c the environment provided by the region server
    * @param store the store where compaction is being requested
    * @param scanner the scanner over existing data used in the store file
    * @return the scanner to use during compaction.  Should not be {@code null}
    * unless the implementation is writing new store files on its own.
    * @throws IOException if an error occurred on the coprocessor
    */
   InternalScanner preFlush(final ObserverContext<RegionCoprocessorEnvironment> c, final Store store,
       final InternalScanner scanner) throws IOException;
 
   /**
    * Called after the memstore is flushed to disk.
    * @param c the environment provided by the region server
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated use {@link #preFlush(ObserverContext, Store, InternalScanner)} instead.
    */
   void postFlush(final ObserverContext<RegionCoprocessorEnvironment> c) throws IOException;
 
   /**
    * Called after a Store's memstore is flushed to disk.
    * @param c the environment provided by the region server
    * @param store the store being flushed
    * @param resultFile the new store file written out during compaction
    * @throws IOException if an error occurred on the coprocessor
    */
   void postFlush(final ObserverContext<RegionCoprocessorEnvironment> c, final Store store,
       final StoreFile resultFile) throws IOException;
 
   /**
    * Called prior to selecting the {@link StoreFile StoreFiles} to compact from the list of
    * available candidates. To alter the files used for compaction, you may mutate the passed in list
    * of candidates.
    * @param c the environment provided by the region server
    * @param store the store where compaction is being requested
    * @param candidates the store files currently available for compaction
    * @param request custom compaction request
    * @throws IOException if an error occurred on the coprocessor
    */
   void preCompactSelection(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final List<StoreFile> candidates, final CompactionRequest request)
       throws IOException;
 
   /**
    * Called prior to selecting the {@link StoreFile}s to compact from the list of available
    * candidates. To alter the files used for compaction, you may mutate the passed in list of
    * candidates.
    * @param c the environment provided by the region server
    * @param store the store where compaction is being requested
    * @param candidates the store files currently available for compaction
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated Use {@link #preCompactSelection(ObserverContext, Store, List, CompactionRequest)}
    *             instead
    */
   @Deprecated
   void preCompactSelection(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final List<StoreFile> candidates) throws IOException;
 
   /**
    * Called after the {@link StoreFile}s to compact have been selected from the available
    * candidates.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param selected the store files selected to compact
    * @param request custom compaction request
    */
   void postCompactSelection(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final ImmutableList<StoreFile> selected, CompactionRequest request);
 
   /**
    * Called after the {@link StoreFile}s to compact have been selected from the available
    * candidates.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param selected the store files selected to compact
    * @deprecated use {@link #postCompactSelection(ObserverContext, Store, ImmutableList,
    *             CompactionRequest)} instead.
    */
   @Deprecated
   void postCompactSelection(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final ImmutableList<StoreFile> selected);
 
   /**
    * Called prior to writing the {@link StoreFile}s selected for compaction into a new
    * {@code StoreFile}. To override or modify the compaction process, implementing classes have two
    * options:
    * <ul>
    * <li>Wrap the provided {@link InternalScanner} with a custom implementation that is returned
    * from this method. The custom scanner can then inspect 
    * {@link org.apache.hadoop.hbase.KeyValue}s from the wrapped
    * scanner, applying its own policy to what gets written.</li>
    * <li>Call {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} and provide a
    * custom implementation for writing of new {@link StoreFile}s. <strong>Note: any implementations
    * bypassing core compaction using this approach must write out new store files themselves or the
    * existing data will no longer be available after compaction.</strong></li>
    * </ul>
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param scanner the scanner over existing data used in the store file rewriting
    * @param scanType type of Scan
    * @param request the requested compaction
    * @return the scanner to use during compaction. Should not be {@code null} unless the
    *         implementation is writing new store files on its own.
    * @throws IOException if an error occurred on the coprocessor
    */
   InternalScanner preCompact(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final InternalScanner scanner, final ScanType scanType,
       CompactionRequest request) throws IOException;
 
   /**
    * Called prior to writing the {@link StoreFile}s selected for compaction into a new
    * {@code StoreFile}. To override or modify the compaction process, implementing classes have two
    * options:
    * <ul>
    * <li>Wrap the provided {@link InternalScanner} with a custom implementation that is returned
    * from this method. The custom scanner can then inspect 
    * {@link org.apache.hadoop.hbase.KeyValue}s from the wrapped
    * scanner, applying its own policy to what gets written.</li>
    * <li>Call {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} and provide a
    * custom implementation for writing of new {@link StoreFile}s. <strong>Note: any implementations
    * bypassing core compaction using this approach must write out new store files themselves or the
    * existing data will no longer be available after compaction.</strong></li>
    * </ul>
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param scanner the scanner over existing data used in the store file rewriting
    * @param scanType type of Scan
    * @return the scanner to use during compaction. Should not be {@code null} unless the
    *         implementation is writing new store files on its own.
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated use
    *             {@link #preCompact(ObserverContext, Store, InternalScanner,
    *             ScanType, CompactionRequest)} instead
    */
   @Deprecated
   InternalScanner preCompact(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final InternalScanner scanner, final ScanType scanType) throws IOException;
 
   /**
    * Called prior to writing the {@link StoreFile}s selected for compaction into a new
    * {@code StoreFile} and prior to creating the scanner used to read the input files. To override
    * or modify the compaction process, implementing classes can return a new scanner to provide the
    * KeyValues to be stored into the new {@code StoreFile} or null to perform the default
    * processing. Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param scanners the list {@link org.apache.hadoop.hbase.regionserver.StoreFileScanner}s 
    *        to be read from
    * @param scanType the {@link ScanType} indicating whether this is a major or minor compaction
    * @param earliestPutTs timestamp of the earliest put that was found in any of the involved store
    *          files
    * @param s the base scanner, if not {@code null}, from previous RegionObserver in the chain
    * @param request the requested compaction
    * @return the scanner to use during compaction. {@code null} if the default implementation is to
    *         be used.
    * @throws IOException if an error occurred on the coprocessor
    */
   InternalScanner preCompactScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, List<? extends KeyValueScanner> scanners, final ScanType scanType,
       final long earliestPutTs, final InternalScanner s, CompactionRequest request)
       throws IOException;
 
   /**
    * Called prior to writing the {@link StoreFile}s selected for compaction into a new
    * {@code StoreFile} and prior to creating the scanner used to read the input files. To override
    * or modify the compaction process, implementing classes can return a new scanner to provide the
    * KeyValues to be stored into the new {@code StoreFile} or null to perform the default
    * processing. Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param scanners the list {@link org.apache.hadoop.hbase.regionserver.StoreFileScanner}s 
    *        to be read from
    * @param scanType the {@link ScanType} indicating whether this is a major or minor compaction
    * @param earliestPutTs timestamp of the earliest put that was found in any of the involved store
    *          files
    * @param s the base scanner, if not {@code null}, from previous RegionObserver in the chain
    * @return the scanner to use during compaction. {@code null} if the default implementation is to
    *         be used.
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated Use
    *             {@link #preCompactScannerOpen(ObserverContext, Store, List, ScanType, long,
    *             InternalScanner, CompactionRequest)} instead.
    */
   @Deprecated
   InternalScanner preCompactScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, List<? extends KeyValueScanner> scanners, final ScanType scanType,
       final long earliestPutTs, final InternalScanner s) throws IOException;
 
   /**
    * Called after compaction has completed and the new store file has been moved in to place.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param resultFile the new store file written out during compaction
    * @param request the requested compaction
    * @throws IOException if an error occurred on the coprocessor
    */
   void postCompact(final ObserverContext<RegionCoprocessorEnvironment> c, final Store store,
       StoreFile resultFile, CompactionRequest request) throws IOException;
 
   /**
    * Called after compaction has completed and the new store file has been moved in to place.
    * @param c the environment provided by the region server
    * @param store the store being compacted
    * @param resultFile the new store file written out during compaction
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated Use {@link #postCompact(ObserverContext, Store, StoreFile, CompactionRequest)}
    *             instead
    */
   @Deprecated
   void postCompact(final ObserverContext<RegionCoprocessorEnvironment> c, final Store store,
       StoreFile resultFile) throws IOException;
 
   /**
    * Called before the region is split.
    * @param c the environment provided by the region server
    * (e.getRegion() returns the parent region)
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated Use preSplit(
    *    final ObserverContext&lt;RegionCoprocessorEnvironment&gt; c, byte[] splitRow)
    */
   void preSplit(final ObserverContext<RegionCoprocessorEnvironment> c) throws IOException;
 
   /**
    * Called before the region is split.
    * @param c the environment provided by the region server
    * (e.getRegion() returns the parent region)
    * @throws IOException if an error occurred on the coprocessor
    */
   void preSplit(final ObserverContext<RegionCoprocessorEnvironment> c, byte[] splitRow)
       throws IOException;
 
   /**
    * Called after the region is split.
    * @param c the environment provided by the region server
    * (e.getRegion() returns the parent region)
    * @param l the left daughter region
    * @param r the right daughter region
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated Use postCompleteSplit() instead
    */
   void postSplit(final ObserverContext<RegionCoprocessorEnvironment> c, final Region l,
       final Region r) throws IOException;
 
   /**
    * This will be called before PONR step as part of split transaction. Calling
    * {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} rollback the split
    * @param ctx
    * @param splitKey
    * @param metaEntries
    * @throws IOException
    */
   void preSplitBeforePONR(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       byte[] splitKey, List<Mutation> metaEntries) throws IOException;
 
   
   /**
    * This will be called after PONR step as part of split transaction
    * Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param ctx
    * @throws IOException
    */
   void preSplitAfterPONR(final ObserverContext<RegionCoprocessorEnvironment> ctx) throws IOException;
   
   /**
    * This will be called before the roll back of the split region is completed 
    * @param ctx
    * @throws IOException
    */
   void preRollBackSplit(final ObserverContext<RegionCoprocessorEnvironment> ctx) throws IOException;
 
   /**
    * This will be called after the roll back of the split region is completed
    * @param ctx
    * @throws IOException
    */
   void postRollBackSplit(final ObserverContext<RegionCoprocessorEnvironment> ctx)
     throws IOException;
 
   /**
    * Called after any split request is processed.  This will be called irrespective of success or
    * failure of the split.
    * @param ctx
    * @throws IOException
    */
   void postCompleteSplit(final ObserverContext<RegionCoprocessorEnvironment> ctx)
     throws IOException;
   /**
    * Called before the region is reported as closed to the master.
    * @param c the environment provided by the region server
    * @param abortRequested true if the region server is aborting
    * @throws IOException 
    */
   void preClose(final ObserverContext<RegionCoprocessorEnvironment> c,
       boolean abortRequested) throws IOException;
 
   /**
    * Called after the region is reported as closed to the master.
    * @param c the environment provided by the region server
    * @param abortRequested true if the region server is aborting
    */
   void postClose(final ObserverContext<RegionCoprocessorEnvironment> c,
       boolean abortRequested);
 
   /**
    * Called before a client makes a GetClosestRowBefore request.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row the row
    * @param family the family
    * @param result The result to return to the client if default processing
    * is bypassed. Can be modified. Will not be used if default processing
    * is not bypassed.
    * @throws IOException if an error occurred on the coprocessor
    */
   void preGetClosestRowBefore(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final Result result)
     throws IOException;
 
   /**
    * Called after a client makes a GetClosestRowBefore request.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row the row
    * @param family the desired family
    * @param result the result to return to the client, modify as necessary
    * @throws IOException if an error occurred on the coprocessor
    */
   void postGetClosestRowBefore(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final Result result)
     throws IOException;
 
   /**
    * Called before the client performs a Get
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param get the Get request
    * @param result The result to return to the client if default processing
    * is bypassed. Can be modified. Will not be used if default processing
    * is not bypassed.
    * @throws IOException if an error occurred on the coprocessor
    */
   void preGetOp(final ObserverContext<RegionCoprocessorEnvironment> c, final Get get,
       final List<Cell> result)
     throws IOException;
 
   /**
    * Called after the client performs a Get
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param get the Get request
    * @param result the result to return to the client, modify as necessary
    * @throws IOException if an error occurred on the coprocessor
    */
   void postGetOp(final ObserverContext<RegionCoprocessorEnvironment> c, final Get get,
       final List<Cell> result)
     throws IOException;
 
   /**
    * Called before the client tests for existence using a Get.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param get the Get request
    * @param exists
    * @return the value to return to the client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preExists(final ObserverContext<RegionCoprocessorEnvironment> c, final Get get,
       final boolean exists)
     throws IOException;
 
   /**
    * Called after the client tests for existence using a Get.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param get the Get request
    * @param exists the result returned by the region server
    * @return the result to return to the client
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean postExists(final ObserverContext<RegionCoprocessorEnvironment> c, final Get get,
       final boolean exists)
     throws IOException;
 
   /**
    * Called before the client stores a value.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param put The Put object
    * @param edit The WALEdit object that will be written to the wal
    * @param durability Persistence guarantee for this Put
    * @throws IOException if an error occurred on the coprocessor
    */
   void prePut(final ObserverContext<RegionCoprocessorEnvironment> c, 
       final Put put, final WALEdit edit, final Durability durability)
     throws IOException;
 
   /**
    * Called after the client stores a value.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param put The Put object
    * @param edit The WALEdit object for the wal
    * @param durability Persistence guarantee for this Put
    * @throws IOException if an error occurred on the coprocessor
    */
   void postPut(final ObserverContext<RegionCoprocessorEnvironment> c, 
       final Put put, final WALEdit edit, final Durability durability)
     throws IOException;
 
   /**
    * Called before the client deletes a value.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param delete The Delete object
    * @param edit The WALEdit object for the wal
    * @param durability Persistence guarantee for this Delete
    * @throws IOException if an error occurred on the coprocessor
    */
   void preDelete(final ObserverContext<RegionCoprocessorEnvironment> c, 
       final Delete delete, final WALEdit edit, final Durability durability)
     throws IOException;
 /**
  * Called before the server updates the timestamp for version delete with latest timestamp.
  * <p>
  * Call CoprocessorEnvironment#bypass to skip default actions
  * <p>
  * Call CoprocessorEnvironment#complete to skip any subsequent chained
  * coprocessors
  * @param c the environment provided by the region server
  * @param mutation - the parent mutation associated with this delete cell
  * @param cell - The deleteColumn with latest version cell
  * @param byteNow - timestamp bytes
  * @param get - the get formed using the current cell's row.
  * Note that the get does not specify the family and qualifier
  * @throws IOException
  */
   void prePrepareTimeStampForDeleteVersion(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Mutation mutation, final Cell cell, final byte[] byteNow,
       final Get get) throws IOException;
 
   /**
    * Called after the client deletes a value.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param delete The Delete object
    * @param edit The WALEdit object for the wal
    * @param durability Persistence guarantee for this Delete
    * @throws IOException if an error occurred on the coprocessor
    */
   void postDelete(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Delete delete, final WALEdit edit, final Durability durability)
     throws IOException;
   
   /**
    * This will be called for every batch mutation operation happening at the server. This will be
    * called after acquiring the locks on the mutating rows and after applying the proper timestamp
    * for each Mutation at the server. The batch may contain Put/Delete. By setting OperationStatus
    * of Mutations ({@link MiniBatchOperationInProgress#setOperationStatus(int, OperationStatus)}),
    * {@link RegionObserver} can make Region to skip these Mutations.
    * @param c the environment provided by the region server
    * @param miniBatchOp batch of Mutations getting applied to region.
    * @throws IOException if an error occurred on the coprocessor
    */
   void preBatchMutate(final ObserverContext<RegionCoprocessorEnvironment> c,
       final MiniBatchOperationInProgress<Mutation> miniBatchOp) throws IOException;
 
   /**
    * This will be called after applying a batch of Mutations on a region. The Mutations are added to
    * memstore and WAL.
    * @param c the environment provided by the region server
    * @param miniBatchOp batch of Mutations applied to region.
    * @throws IOException if an error occurred on the coprocessor
    */
   void postBatchMutate(final ObserverContext<RegionCoprocessorEnvironment> c,
       final MiniBatchOperationInProgress<Mutation> miniBatchOp) throws IOException;
 
   /**
    * This will be called for region operations where read lock is acquired in
    * {@link Region#startRegionOperation()}.
    * @param ctx
    * @param operation The operation is about to be taken on the region
    * @throws IOException
    */
   void postStartRegionOperation(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       Operation operation) throws IOException;
 
   /**
    * Called after releasing read lock in {@link Region#closeRegionOperation()}.
    * @param ctx
    * @param operation
    * @throws IOException
    */
   void postCloseRegionOperation(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       Operation operation) throws IOException;
 
   /**
    * Called after the completion of batch put/delete and will be called even if the batch operation
    * fails
    * @param ctx
    * @param miniBatchOp 
    * @param success true if batch operation is successful otherwise false.
    * @throws IOException
    */
   void postBatchMutateIndispensably(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       MiniBatchOperationInProgress<Mutation> miniBatchOp, final boolean success) throws IOException;
 
   /**
    * Called before checkAndPut.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param put data to put if check succeeds
    * @param result 
    * @return the return value to return to client if bypassing default
    * processing
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preCheckAndPut(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final CompareOp compareOp, final ByteArrayComparable comparator,
       final Put put, final boolean result)
     throws IOException;
 
   /**
    * Called before checkAndPut but after acquiring rowlock.
    * <p>
    * <b>Note:</b> Caution to be taken for not doing any long time operation in this hook. 
    * Row will be locked for longer time. Trying to acquire lock on another row, within this, 
    * can lead to potential deadlock.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param put data to put if check succeeds
    * @param result 
    * @return the return value to return to client if bypassing default
    * processing
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preCheckAndPutAfterRowLock(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte[] row, final byte[] family, final byte[] qualifier, final CompareOp compareOp,
       final ByteArrayComparable comparator, final Put put, 
       final boolean result) throws IOException;
 
   /**
    * Called after checkAndPut
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param put data to put if check succeeds
    * @param result from the checkAndPut
    * @return the possibly transformed return value to return to client
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean postCheckAndPut(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final CompareOp compareOp, final ByteArrayComparable comparator,
       final Put put, final boolean result)
     throws IOException;
 
   /**
    * Called before checkAndDelete.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param delete delete to commit if check succeeds
    * @param result 
    * @return the value to return to client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preCheckAndDelete(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final CompareOp compareOp, final ByteArrayComparable comparator,
       final Delete delete, final boolean result)
     throws IOException;
 
   /**
    * Called before checkAndDelete but after acquiring rowock.
    * <p>
    * <b>Note:</b> Caution to be taken for not doing any long time operation in this hook. 
    * Row will be locked for longer time. Trying to acquire lock on another row, within this, 
    * can lead to potential deadlock.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param delete delete to commit if check succeeds
    * @param result 
    * @return the value to return to client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preCheckAndDeleteAfterRowLock(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte[] row, final byte[] family, final byte[] qualifier, final CompareOp compareOp,
       final ByteArrayComparable comparator, final Delete delete,
       final boolean result) throws IOException;
 
   /**
    * Called after checkAndDelete
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param compareOp the comparison operation
    * @param comparator the comparator
    * @param delete delete to commit if check succeeds
    * @param result from the CheckAndDelete
    * @return the possibly transformed returned value to return to client
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean postCheckAndDelete(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final CompareOp compareOp, final ByteArrayComparable comparator,
       final Delete delete, final boolean result)
     throws IOException;
 
   /**
    * Called before incrementColumnValue
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param amount long amount to increment
    * @param writeToWAL true if the change should be written to the WAL
    * @return value to return to the client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated This hook is no longer called by the RegionServer
    */
   @Deprecated
   long preIncrementColumnValue(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final long amount, final boolean writeToWAL)
     throws IOException;
 
   /**
    * Called after incrementColumnValue
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param row row to check
    * @param family column family
    * @param qualifier column qualifier
    * @param amount long amount to increment
    * @param writeToWAL true if the change should be written to the WAL
    * @param result the result returned by incrementColumnValue
    * @return the result to return to the client
    * @throws IOException if an error occurred on the coprocessor
    * @deprecated This hook is no longer called by the RegionServer
    */
   @Deprecated
   long postIncrementColumnValue(final ObserverContext<RegionCoprocessorEnvironment> c,
       final byte [] row, final byte [] family, final byte [] qualifier,
       final long amount, final boolean writeToWAL, final long result)
     throws IOException;
 
   /**
    * Called before Append.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param append Append object
    * @return result to return to the client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   Result preAppend(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Append append)
     throws IOException;
 
   /**
    * Called before Append but after acquiring rowlock.
    * <p>
    * <b>Note:</b> Caution to be taken for not doing any long time operation in this hook. 
    * Row will be locked for longer time. Trying to acquire lock on another row, within this, 
    * can lead to potential deadlock.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param append Append object
    * @return result to return to the client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   Result preAppendAfterRowLock(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Append append) throws IOException;
 
   /**
    * Called after Append
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param append Append object
    * @param result the result returned by increment
    * @return the result to return to the client
    * @throws IOException if an error occurred on the coprocessor
    */
   Result postAppend(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Append append, final Result result)
     throws IOException;
 
   /**
    * Called before Increment.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param increment increment object
    * @return result to return to the client if bypassing default processing
    * @throws IOException if an error occurred on the coprocessor
    */
   Result preIncrement(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Increment increment)
     throws IOException;
 
   /**
    * Called before Increment but after acquiring rowlock.
    * <p>
    * <b>Note:</b> Caution to be taken for not doing any long time operation in this hook. 
    * Row will be locked for longer time. Trying to acquire lock on another row, within this, 
    * can lead to potential deadlock.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained coprocessors
    * 
    * @param c
    *          the environment provided by the region server
    * @param increment
    *          increment object
    * @return result to return to the client if bypassing default processing
    * @throws IOException
    *           if an error occurred on the coprocessor
    */
   Result preIncrementAfterRowLock(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Increment increment) throws IOException;
 
   /**
    * Called after increment
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param increment increment object
    * @param result the result returned by increment
    * @return the result to return to the client
    * @throws IOException if an error occurred on the coprocessor
    */
   Result postIncrement(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Increment increment, final Result result)
     throws IOException;
 
   /**
    * Called before the client opens a new scanner.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param scan the Scan specification
    * @param s if not null, the base scanner
    * @return an RegionScanner instance to use instead of the base scanner if
    * overriding default behavior, null otherwise
    * @throws IOException if an error occurred on the coprocessor
    */
   RegionScanner preScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Scan scan, final RegionScanner s)
     throws IOException;
 
   /**
    * Called before a store opens a new scanner.
    * This hook is called when a "user" scanner is opened.
    * <p>
    * See {@link #preFlushScannerOpen(ObserverContext, Store, KeyValueScanner, InternalScanner)}
    * and {@link #preCompactScannerOpen(ObserverContext,
    *  Store, List, ScanType, long, InternalScanner)}
    * to override scanners created for flushes or compactions, resp.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors.
    * Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param c the environment provided by the region server
    * @param store the store being scanned
    * @param scan the Scan specification
    * @param targetCols columns to be used in the scanner
    * @param s the base scanner, if not {@code null}, from previous RegionObserver in the chain
    * @return a KeyValueScanner instance to use or {@code null} to use the default implementation
    * @throws IOException if an error occurred on the coprocessor
    */
   KeyValueScanner preStoreScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Store store, final Scan scan, final NavigableSet<byte[]> targetCols,
       final KeyValueScanner s) throws IOException;
 
   /**
    * Called after the client opens a new scanner.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param scan the Scan specification
    * @param s if not null, the base scanner
    * @return the scanner instance to use
    * @throws IOException if an error occurred on the coprocessor
    */
   RegionScanner postScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
       final Scan scan, final RegionScanner s)
     throws IOException;
 
   /**
    * Called before the client asks for the next row on a scanner.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param s the scanner
    * @param result The result to return to the client if default processing
    * is bypassed. Can be modified. Will not be returned if default processing
    * is not bypassed.
    * @param limit the maximum number of results to return
    * @param hasNext the 'has more' indication
    * @return 'has more' indication that should be sent to client
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean preScannerNext(final ObserverContext<RegionCoprocessorEnvironment> c,
       final InternalScanner s, final List<Result> result,
       final int limit, final boolean hasNext)
     throws IOException;
 
   /**
    * Called after the client asks for the next row on a scanner.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param s the scanner
    * @param result the result to return to the client, can be modified
    * @param limit the maximum number of results to return
    * @param hasNext the 'has more' indication
    * @return 'has more' indication that should be sent to client
    * @throws IOException if an error occurred on the coprocessor
    */
   boolean postScannerNext(final ObserverContext<RegionCoprocessorEnvironment> c,
       final InternalScanner s, final List<Result> result, final int limit,
       final boolean hasNext)
     throws IOException;
 
   /**
    * This will be called by the scan flow when the current scanned row is being filtered out by the
    * filter. The filter may be filtering out the row via any of the below scenarios
    * <ol>
    * <li>
    * <code>boolean filterRowKey(byte [] buffer, int offset, int length)</code> returning true</li>
    * <li>
    * <code>boolean filterRow()</code> returning true</li>
    * <li>
    * <code>void filterRow(List&lt;KeyValue&gt; kvs)</code> removing all the kvs
    * from the passed List</li>
    * </ol>
    * @param c the environment provided by the region server
    * @param s the scanner
    * @param currentRow The current rowkey which got filtered out
    * @param offset offset to rowkey
    * @param length length of rowkey
    * @param hasMore the 'has more' indication
    * @return whether more rows are available for the scanner or not
    * @throws IOException
    */
   boolean postScannerFilterRow(final ObserverContext<RegionCoprocessorEnvironment> c,
       final InternalScanner s, final byte[] currentRow, final int offset, final short length,
       final boolean hasMore) throws IOException;
 
   /**
    * Called before the client closes a scanner.
    * <p>
    * Call CoprocessorEnvironment#bypass to skip default actions
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param s the scanner
    * @throws IOException if an error occurred on the coprocessor
    */
   void preScannerClose(final ObserverContext<RegionCoprocessorEnvironment> c,
       final InternalScanner s)
     throws IOException;
 
   /**
    * Called after the client closes a scanner.
    * <p>
    * Call CoprocessorEnvironment#complete to skip any subsequent chained
    * coprocessors
    * @param c the environment provided by the region server
    * @param s the scanner
    * @throws IOException if an error occurred on the coprocessor
    */
   void postScannerClose(final ObserverContext<RegionCoprocessorEnvironment> c,
       final InternalScanner s)
     throws IOException;
 
   /**
    * Called before a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
    * replayed for this region.
    */
   void preWALRestore(final ObserverContext<? extends RegionCoprocessorEnvironment> ctx,
       HRegionInfo info, WALKey logKey, WALEdit logEdit) throws IOException;
 
   /**
    * Called before a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
    * replayed for this region.
    *
    * This method is left in place to maintain binary compatibility with older
    * {@link RegionObserver}s. If an implementation directly overrides
    * {@link #preWALRestore(ObserverContext, HRegionInfo, WALKey, WALEdit)} then this version
    * won't be called at all, barring problems with the Security Manager. To work correctly
    * in the presence of a strict Security Manager, or in the case of an implementation that
    * relies on a parent class to implement preWALRestore, you should implement this method
    * as a call to the non-deprecated version.
    *
    * Users of this method will see all edits that can be treated as HLogKey. If there are
    * edits that can't be treated as HLogKey they won't be offered to coprocessors that rely
    * on this method. If a coprocessor gets skipped because of this mechanism, a log message
    * at ERROR will be generated per coprocessor on the logger for {@link CoprocessorHost} once per
    * classloader.
    *
    * @deprecated use {@link #preWALRestore(ObserverContext, HRegionInfo, WALKey, WALEdit)}
    */
   @Deprecated
   void preWALRestore(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
 
   /**
    * Called after a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
    * replayed for this region.
    */
   void postWALRestore(final ObserverContext<? extends RegionCoprocessorEnvironment> ctx,
       HRegionInfo info, WALKey logKey, WALEdit logEdit) throws IOException;
 
   /**
    * Called after a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
    * replayed for this region.
    *
    * This method is left in place to maintain binary compatibility with older
    * {@link RegionObserver}s. If an implementation directly overrides
    * {@link #postWALRestore(ObserverContext, HRegionInfo, WALKey, WALEdit)} then this version
    * won't be called at all, barring problems with the Security Manager. To work correctly
    * in the presence of a strict Security Manager, or in the case of an implementation that
    * relies on a parent class to implement preWALRestore, you should implement this method
    * as a call to the non-deprecated version.
    *
    * Users of this method will see all edits that can be treated as HLogKey. If there are
    * edits that can't be treated as HLogKey they won't be offered to coprocessors that rely
    * on this method. If a coprocessor gets skipped because of this mechanism, a log message
    * at ERROR will be generated per coprocessor on the logger for {@link CoprocessorHost} once per
    * classloader.
    *
    * @deprecated use {@link #postWALRestore(ObserverContext, HRegionInfo, WALKey, WALEdit)}
    */
   @Deprecated
   void postWALRestore(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
 
   /**
    * Called before bulkLoadHFile. Users can create a StoreFile instance to
    * access the contents of a HFile.
    *
    * @param ctx
    * @param familyPaths pairs of { CF, HFile path } submitted for bulk load. Adding
    * or removing from this list will add or remove HFiles to be bulk loaded.
    * @throws IOException
    */
   void preBulkLoadHFile(final ObserverContext<RegionCoprocessorEnvironment> ctx,
     List<Pair<byte[], String>> familyPaths) throws IOException;
 
   /**
    * Called after bulkLoadHFile.
    *
    * @param ctx
    * @param familyPaths pairs of { CF, HFile path } submitted for bulk load
    * @param hasLoaded whether the bulkLoad was successful
    * @return the new value of hasLoaded
    * @throws IOException
    */
   boolean postBulkLoadHFile(final ObserverContext<RegionCoprocessorEnvironment> ctx,
     List<Pair<byte[], String>> familyPaths, boolean hasLoaded) throws IOException;
 
   /**
    * Called before creation of Reader for a store file.
    * Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * 
    * @param ctx the environment provided by the region server
    * @param fs fileystem to read from
    * @param p path to the file
    * @param in {@link FSDataInputStreamWrapper}
    * @param size Full size of the file
    * @param cacheConf
    * @param r original reference file. This will be not null only when reading a split file.
    * @param reader the base reader, if not {@code null}, from previous RegionObserver in the chain
    * @return a Reader instance to use instead of the base reader if overriding
    * default behavior, null otherwise
    * @throws IOException
    */
   StoreFile.Reader preStoreFileReaderOpen(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       final FileSystem fs, final Path p, final FSDataInputStreamWrapper in, long size,
       final CacheConfig cacheConf, final Reference r, StoreFile.Reader reader) throws IOException;
 
   /**
    * Called after the creation of Reader for a store file.
    * 
    * @param ctx the environment provided by the region server
    * @param fs fileystem to read from
    * @param p path to the file
    * @param in {@link FSDataInputStreamWrapper}
    * @param size Full size of the file
    * @param cacheConf
    * @param r original reference file. This will be not null only when reading a split file.
    * @param reader the base reader instance
    * @return The reader to use
    * @throws IOException
    */
   StoreFile.Reader postStoreFileReaderOpen(final ObserverContext<RegionCoprocessorEnvironment> ctx,
       final FileSystem fs, final Path p, final FSDataInputStreamWrapper in, long size,
       final CacheConfig cacheConf, final Reference r, StoreFile.Reader reader) throws IOException;
 
   /**
    * Called after a new cell has been created during an increment operation, but before
    * it is committed to the WAL or memstore.
    * Calling {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} has no
    * effect in this hook.
    * @param ctx the environment provided by the region server
    * @param opType the operation type
    * @param mutation the current mutation
    * @param oldCell old cell containing previous value
    * @param newCell the new cell containing the computed value
    * @return the new cell, possibly changed
    * @throws IOException
    */
   Cell postMutationBeforeWAL(ObserverContext<RegionCoprocessorEnvironment> ctx,
       MutationType opType, Mutation mutation, Cell oldCell, Cell newCell) throws IOException;
 
   /**
    * Called after the ScanQueryMatcher creates ScanDeleteTracker. Implementing
    * this hook would help in creating customised DeleteTracker and returning
    * the newly created DeleteTracker
    *
    * @param ctx the environment provided by the region server
    * @param delTracker the deleteTracker that is created by the QueryMatcher
    * @return the Delete Tracker
    * @throws IOException
    */
   DeleteTracker postInstantiateDeleteTracker(
       final ObserverContext<RegionCoprocessorEnvironment> ctx, DeleteTracker delTracker)
       throws IOException;
 }