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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.client;
19  
20  import java.io.IOException;
21  import java.io.InterruptedIOException;
22  import java.util.ArrayList;
23  import java.util.Arrays;
24  import java.util.LinkedList;
25  import java.util.List;
26  import java.util.concurrent.ExecutorService;
27  
28  import org.apache.commons.logging.Log;
29  import org.apache.commons.logging.LogFactory;
30  import org.apache.hadoop.conf.Configuration;
31  import org.apache.hadoop.hbase.Cell;
32  import org.apache.hadoop.hbase.CellUtil;
33  import org.apache.hadoop.hbase.DoNotRetryIOException;
34  import org.apache.hadoop.hbase.HBaseConfiguration;
35  import org.apache.hadoop.hbase.HConstants;
36  import org.apache.hadoop.hbase.HRegionInfo;
37  import org.apache.hadoop.hbase.NotServingRegionException;
38  import org.apache.hadoop.hbase.TableName;
39  import org.apache.hadoop.hbase.UnknownScannerException;
40  import org.apache.hadoop.hbase.classification.InterfaceAudience;
41  import org.apache.hadoop.hbase.exceptions.OutOfOrderScannerNextException;
42  import org.apache.hadoop.hbase.ipc.RpcControllerFactory;
43  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
44  import org.apache.hadoop.hbase.protobuf.generated.MapReduceProtos;
45  import org.apache.hadoop.hbase.regionserver.RegionServerStoppedException;
46  import org.apache.hadoop.hbase.util.Bytes;
47  
48  import com.google.common.annotations.VisibleForTesting;
49  
50  /**
51   * Implements the scanner interface for the HBase client.
52   * If there are multiple regions in a table, this scanner will iterate
53   * through them all.
54   */
55  @InterfaceAudience.Private
56  public class ClientScanner extends AbstractClientScanner {
57      private final Log LOG = LogFactory.getLog(this.getClass());
58      // A byte array in which all elements are the max byte, and it is used to
59      // construct closest front row
60      static byte[] MAX_BYTE_ARRAY = Bytes.createMaxByteArray(9);
61      protected Scan scan;
62      protected boolean closed = false;
63      // Current region scanner is against.  Gets cleared if current region goes
64      // wonky: e.g. if it splits on us.
65      protected HRegionInfo currentRegion = null;
66      protected ScannerCallableWithReplicas callable = null;
67      protected final LinkedList<Result> cache = new LinkedList<Result>();
68      /**
69       * A list of partial results that have been returned from the server. This list should only
70       * contain results if this scanner does not have enough partial results to form the complete
71       * result.
72       */
73      protected final LinkedList<Result> partialResults = new LinkedList<Result>();
74      /**
75       * The row for which we are accumulating partial Results (i.e. the row of the Results stored
76       * inside partialResults). Changes to partialResultsRow and partialResults are kept in sync
77       * via the methods {@link #addToPartialResults(Result)} and {@link #clearPartialResults()}
78       */
79      protected byte[] partialResultsRow = null;
80      protected final int caching;
81      protected long lastNext;
82      // Keep lastResult returned successfully in case we have to reset scanner.
83      protected Result lastResult = null;
84      protected final long maxScannerResultSize;
85      private final ClusterConnection connection;
86      private final TableName tableName;
87      protected final int scannerTimeout;
88      protected boolean scanMetricsPublished = false;
89      protected RpcRetryingCaller<Result []> caller;
90      protected RpcControllerFactory rpcControllerFactory;
91      protected Configuration conf;
92      //The timeout on the primary. Applicable if there are multiple replicas for a region
93      //In that case, we will only wait for this much timeout on the primary before going
94      //to the replicas and trying the same scan. Note that the retries will still happen
95      //on each replica and the first successful results will be taken. A timeout of 0 is
96      //disallowed.
97      protected final int primaryOperationTimeout;
98      private int retries;
99      protected final ExecutorService pool;
100 
101   /**
102    * Create a new ClientScanner for the specified table Note that the passed {@link Scan}'s start
103    * row maybe changed changed.
104    * @param conf The {@link Configuration} to use.
105    * @param scan {@link Scan} to use in this scanner
106    * @param tableName The table that we wish to scan
107    * @param connection Connection identifying the cluster
108    * @throws IOException
109    */
110   public ClientScanner(final Configuration conf, final Scan scan, final TableName tableName,
111       ClusterConnection connection, RpcRetryingCallerFactory rpcFactory,
112       RpcControllerFactory controllerFactory, ExecutorService pool, int primaryOperationTimeout)
113       throws IOException {
114       if (LOG.isTraceEnabled()) {
115         LOG.trace("Scan table=" + tableName
116             + ", startRow=" + Bytes.toStringBinary(scan.getStartRow()));
117       }
118       this.scan = scan;
119       this.tableName = tableName;
120       this.lastNext = System.currentTimeMillis();
121       this.connection = connection;
122       this.pool = pool;
123       this.primaryOperationTimeout = primaryOperationTimeout;
124       this.retries = conf.getInt(HConstants.HBASE_CLIENT_RETRIES_NUMBER,
125           HConstants.DEFAULT_HBASE_CLIENT_RETRIES_NUMBER);
126       if (scan.getMaxResultSize() > 0) {
127         this.maxScannerResultSize = scan.getMaxResultSize();
128       } else {
129         this.maxScannerResultSize = conf.getLong(
130           HConstants.HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE_KEY,
131           HConstants.DEFAULT_HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE);
132       }
133       this.scannerTimeout = HBaseConfiguration.getInt(conf,
134         HConstants.HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD,
135         HConstants.HBASE_REGIONSERVER_LEASE_PERIOD_KEY,
136         HConstants.DEFAULT_HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD);
137 
138       // check if application wants to collect scan metrics
139       initScanMetrics(scan);
140 
141       // Use the caching from the Scan.  If not set, use the default cache setting for this table.
142       if (this.scan.getCaching() > 0) {
143         this.caching = this.scan.getCaching();
144       } else {
145         this.caching = conf.getInt(
146             HConstants.HBASE_CLIENT_SCANNER_CACHING,
147             HConstants.DEFAULT_HBASE_CLIENT_SCANNER_CACHING);
148       }
149 
150       this.caller = rpcFactory.<Result[]> newCaller();
151       this.rpcControllerFactory = controllerFactory;
152 
153       this.conf = conf;
154       initializeScannerInConstruction();
155     }
156 
157     protected void initializeScannerInConstruction() throws IOException{
158       // initialize the scanner
159       nextScanner(this.caching, false);
160     }
161 
162     protected ClusterConnection getConnection() {
163       return this.connection;
164     }
165 
166     /**
167      * @return Table name
168      * @deprecated As of release 0.96
169      *             (<a href="https://issues.apache.org/jira/browse/HBASE-9508">HBASE-9508</a>).
170      *             This will be removed in HBase 2.0.0. Use {@link #getTable()}.
171      */
172     @Deprecated
173     protected byte [] getTableName() {
174       return this.tableName.getName();
175     }
176 
177     protected TableName getTable() {
178       return this.tableName;
179     }
180 
181     protected int getRetries() {
182       return this.retries;
183     }
184 
185     protected int getScannerTimeout() {
186       return this.scannerTimeout;
187     }
188 
189     protected Configuration getConf() {
190       return this.conf;
191     }
192 
193     protected Scan getScan() {
194       return scan;
195     }
196 
197     protected ExecutorService getPool() {
198       return pool;
199     }
200 
201     protected int getPrimaryOperationTimeout() {
202       return primaryOperationTimeout;
203     }
204 
205     protected int getCaching() {
206       return caching;
207     }
208 
209     protected long getTimestamp() {
210       return lastNext;
211     }
212 
213     @VisibleForTesting
214     protected long getMaxResultSize() {
215       return maxScannerResultSize;
216     }
217 
218     // returns true if the passed region endKey
219     protected boolean checkScanStopRow(final byte [] endKey) {
220       if (this.scan.getStopRow().length > 0) {
221         // there is a stop row, check to see if we are past it.
222         byte [] stopRow = scan.getStopRow();
223         int cmp = Bytes.compareTo(stopRow, 0, stopRow.length,
224           endKey, 0, endKey.length);
225         if (cmp <= 0) {
226           // stopRow <= endKey (endKey is equals to or larger than stopRow)
227           // This is a stop.
228           return true;
229         }
230       }
231       return false; //unlikely.
232     }
233 
234     private boolean possiblyNextScanner(int nbRows, final boolean done) throws IOException {
235       // If we have just switched replica, don't go to the next scanner yet. Rather, try
236       // the scanner operations on the new replica, from the right point in the scan
237       // Note that when we switched to a different replica we left it at a point
238       // where we just did the "openScanner" with the appropriate startrow
239       if (callable != null && callable.switchedToADifferentReplica()) return true;
240       return nextScanner(nbRows, done);
241     }
242 
243     /*
244      * Gets a scanner for the next region.  If this.currentRegion != null, then
245      * we will move to the endrow of this.currentRegion.  Else we will get
246      * scanner at the scan.getStartRow().  We will go no further, just tidy
247      * up outstanding scanners, if <code>currentRegion != null</code> and
248      * <code>done</code> is true.
249      * @param nbRows
250      * @param done Server-side says we're done scanning.
251      */
252   protected boolean nextScanner(int nbRows, final boolean done)
253     throws IOException {
254       // Close the previous scanner if it's open
255       if (this.callable != null) {
256         this.callable.setClose();
257         call(callable, caller, scannerTimeout);
258         this.callable = null;
259       }
260 
261       // Where to start the next scanner
262       byte [] localStartKey;
263 
264       // if we're at end of table, close and return false to stop iterating
265       if (this.currentRegion != null) {
266         byte [] endKey = this.currentRegion.getEndKey();
267         if (endKey == null ||
268             Bytes.equals(endKey, HConstants.EMPTY_BYTE_ARRAY) ||
269             checkScanStopRow(endKey) ||
270             done) {
271           close();
272           if (LOG.isTraceEnabled()) {
273             LOG.trace("Finished " + this.currentRegion);
274           }
275           return false;
276         }
277         localStartKey = endKey;
278         if (LOG.isTraceEnabled()) {
279           LOG.trace("Finished " + this.currentRegion);
280         }
281       } else {
282         localStartKey = this.scan.getStartRow();
283       }
284 
285       if (LOG.isDebugEnabled() && this.currentRegion != null) {
286         // Only worth logging if NOT first region in scan.
287         LOG.debug("Advancing internal scanner to startKey at '" +
288           Bytes.toStringBinary(localStartKey) + "'");
289       }
290       try {
291         callable = getScannerCallable(localStartKey, nbRows);
292         // Open a scanner on the region server starting at the
293         // beginning of the region
294         call(callable, caller, scannerTimeout);
295         this.currentRegion = callable.getHRegionInfo();
296         if (this.scanMetrics != null) {
297           this.scanMetrics.countOfRegions.incrementAndGet();
298         }
299       } catch (IOException e) {
300         close();
301         throw e;
302       }
303       return true;
304     }
305 
306   @VisibleForTesting
307   boolean isAnyRPCcancelled() {
308     return callable.isAnyRPCcancelled();
309   }
310 
311   Result[] call(ScannerCallableWithReplicas callable,
312       RpcRetryingCaller<Result[]> caller, int scannerTimeout)
313       throws IOException, RuntimeException {
314     if (Thread.interrupted()) {
315       throw new InterruptedIOException();
316     }
317     // callWithoutRetries is at this layer. Within the ScannerCallableWithReplicas,
318     // we do a callWithRetries
319     return caller.callWithoutRetries(callable, scannerTimeout);
320   }
321 
322     @InterfaceAudience.Private
323     protected ScannerCallableWithReplicas getScannerCallable(byte [] localStartKey,
324         int nbRows) {
325       scan.setStartRow(localStartKey);
326       ScannerCallable s =
327           new ScannerCallable(getConnection(), getTable(), scan, this.scanMetrics,
328               this.rpcControllerFactory);
329       s.setCaching(nbRows);
330       ScannerCallableWithReplicas sr = new ScannerCallableWithReplicas(tableName, getConnection(),
331        s, pool, primaryOperationTimeout, scan,
332        retries, scannerTimeout, caching, conf, caller);
333       return sr;
334     }
335 
336     /**
337      * Publish the scan metrics. For now, we use scan.setAttribute to pass the metrics back to the
338      * application or TableInputFormat.Later, we could push it to other systems. We don't use
339      * metrics framework because it doesn't support multi-instances of the same metrics on the same
340      * machine; for scan/map reduce scenarios, we will have multiple scans running at the same time.
341      *
342      * By default, scan metrics are disabled; if the application wants to collect them, this
343      * behavior can be turned on by calling calling {@link Scan#setScanMetricsEnabled(boolean)}
344      * 
345      * <p>This invocation clears the scan metrics. Metrics are aggregated in the Scan instance.
346      */
347     protected void writeScanMetrics() {
348       if (this.scanMetrics == null || scanMetricsPublished) {
349         return;
350       }
351       MapReduceProtos.ScanMetrics pScanMetrics = ProtobufUtil.toScanMetrics(scanMetrics);
352       scan.setAttribute(Scan.SCAN_ATTRIBUTES_METRICS_DATA, pScanMetrics.toByteArray());
353       scanMetricsPublished = true;
354     }
355 
356     @Override
357     public Result next() throws IOException {
358       // If the scanner is closed and there's nothing left in the cache, next is a no-op.
359       if (cache.size() == 0 && this.closed) {
360         return null;
361       }
362       if (cache.size() == 0) {
363         loadCache();
364       }
365 
366       if (cache.size() > 0) {
367         return cache.poll();
368       }
369 
370       // if we exhausted this scanner before calling close, write out the scan metrics
371       writeScanMetrics();
372       return null;
373     }
374 
375   @VisibleForTesting
376   public int getCacheSize() {
377     return cache != null ? cache.size() : 0;
378   }
379 
380   /**
381    * Contact the servers to load more {@link Result}s in the cache.
382    */
383   protected void loadCache() throws IOException {
384     Result[] values = null;
385     long remainingResultSize = maxScannerResultSize;
386     int countdown = this.caching;
387 
388     // We need to reset it if it's a new callable that was created
389     // with a countdown in nextScanner
390     callable.setCaching(this.caching);
391     // This flag is set when we want to skip the result returned. We do
392     // this when we reset scanner because it split under us.
393     boolean retryAfterOutOfOrderException = true;
394     // We don't expect that the server will have more results for us if
395     // it doesn't tell us otherwise. We rely on the size or count of results
396     boolean serverHasMoreResults = false;
397     do {
398       try {
399         // Server returns a null values if scanning is to stop. Else,
400         // returns an empty array if scanning is to go on and we've just
401         // exhausted current region.
402         values = call(callable, caller, scannerTimeout);
403         // When the replica switch happens, we need to do certain operations
404         // again. The callable will openScanner with the right startkey
405         // but we need to pick up from there. Bypass the rest of the loop
406         // and let the catch-up happen in the beginning of the loop as it
407         // happens for the cases where we see exceptions. Since only openScanner
408         // would have happened, values would be null
409         if (values == null && callable.switchedToADifferentReplica()) {
410           // Any accumulated partial results are no longer valid since the callable will
411           // openScanner with the correct startkey and we must pick up from there
412           clearPartialResults();
413           this.currentRegion = callable.getHRegionInfo();
414           continue;
415         }
416         retryAfterOutOfOrderException = true;
417       } catch (DoNotRetryIOException e) {
418         // An exception was thrown which makes any partial results that we were collecting
419         // invalid. The scanner will need to be reset to the beginning of a row.
420         clearPartialResults();
421 
422         // DNRIOEs are thrown to make us break out of retries. Some types of DNRIOEs want us
423         // to reset the scanner and come back in again.
424         if (e instanceof UnknownScannerException) {
425           long timeout = lastNext + scannerTimeout;
426           // If we are over the timeout, throw this exception to the client wrapped in
427           // a ScannerTimeoutException. Else, it's because the region moved and we used the old
428           // id against the new region server; reset the scanner.
429           if (timeout < System.currentTimeMillis()) {
430             long elapsed = System.currentTimeMillis() - lastNext;
431             ScannerTimeoutException ex =
432                 new ScannerTimeoutException(elapsed + "ms passed since the last invocation, "
433                     + "timeout is currently set to " + scannerTimeout);
434             ex.initCause(e);
435             throw ex;
436           }
437         } else {
438           // If exception is any but the list below throw it back to the client; else setup
439           // the scanner and retry.
440           Throwable cause = e.getCause();
441           if ((cause != null && cause instanceof NotServingRegionException) ||
442               (cause != null && cause instanceof RegionServerStoppedException) ||
443               e instanceof OutOfOrderScannerNextException) {
444             // Pass
445             // It is easier writing the if loop test as list of what is allowed rather than
446             // as a list of what is not allowed... so if in here, it means we do not throw.
447           } else {
448             throw e;
449           }
450         }
451         // Else, its signal from depths of ScannerCallable that we need to reset the scanner.
452         if (this.lastResult != null) {
453           // The region has moved. We need to open a brand new scanner at
454           // the new location.
455           // Reset the startRow to the row we've seen last so that the new
456           // scanner starts at the correct row. Otherwise we may see previously
457           // returned rows again.
458           // (ScannerCallable by now has "relocated" the correct region)
459           if (scan.isReversed()) {
460             scan.setStartRow(createClosestRowBefore(lastResult.getRow()));
461           } else {
462             scan.setStartRow(Bytes.add(lastResult.getRow(), new byte[1]));
463           }
464         }
465         if (e instanceof OutOfOrderScannerNextException) {
466           if (retryAfterOutOfOrderException) {
467             retryAfterOutOfOrderException = false;
468           } else {
469             // TODO: Why wrap this in a DNRIOE when it already is a DNRIOE?
470             throw new DoNotRetryIOException("Failed after retry of " +
471                 "OutOfOrderScannerNextException: was there a rpc timeout?", e);
472           }
473         }
474         // Clear region.
475         this.currentRegion = null;
476         // Set this to zero so we don't try and do an rpc and close on remote server when
477         // the exception we got was UnknownScanner or the Server is going down.
478         callable = null;
479 
480         // This continue will take us to while at end of loop where we will set up new scanner.
481         continue;
482       }
483       long currentTime = System.currentTimeMillis();
484       if (this.scanMetrics != null) {
485         this.scanMetrics.sumOfMillisSecBetweenNexts.addAndGet(currentTime - lastNext);
486       }
487       lastNext = currentTime;
488       // Groom the array of Results that we received back from the server before adding that
489       // Results to the scanner's cache. If partial results are not allowed to be seen by the
490       // caller, all book keeping will be performed within this method.
491       List<Result> resultsToAddToCache =
492           getResultsToAddToCache(values, callable.isHeartbeatMessage());
493       if (!resultsToAddToCache.isEmpty()) {
494         for (Result rs : resultsToAddToCache) {
495           cache.add(rs);
496           // We don't make Iterator here
497           for (Cell cell : rs.rawCells()) {
498             remainingResultSize -= CellUtil.estimatedHeapSizeOf(cell);
499           }
500           countdown--;
501           this.lastResult = rs;
502         }
503       }
504 
505       // Caller of this method just wants a Result. If we see a heartbeat message, it means
506       // processing of the scan is taking a long time server side. Rather than continue to
507       // loop until a limit (e.g. size or caching) is reached, break out early to avoid causing
508       // unnecesary delays to the caller
509       if (callable.isHeartbeatMessage() && cache.size() > 0) {
510         if (LOG.isTraceEnabled()) {
511           LOG.trace("Heartbeat message received and cache contains Results."
512               + " Breaking out of scan loop");
513         }
514         break;
515       }
516 
517       // We expect that the server won't have more results for us when we exhaust
518       // the size (bytes or count) of the results returned. If the server *does* inform us that
519       // there are more results, we want to avoid possiblyNextScanner(...). Only when we actually
520       // get results is the moreResults context valid.
521       if (null != values && values.length > 0 && callable.hasMoreResultsContext()) {
522         // Only adhere to more server results when we don't have any partialResults
523         // as it keeps the outer loop logic the same.
524         serverHasMoreResults = callable.getServerHasMoreResults() & partialResults.isEmpty();
525       }
526       // Values == null means server-side filter has determined we must STOP
527       // !partialResults.isEmpty() means that we are still accumulating partial Results for a
528       // row. We should not change scanners before we receive all the partial Results for that
529       // row.
530     } while (doneWithRegion(remainingResultSize, countdown, serverHasMoreResults)
531         && (!partialResults.isEmpty() || possiblyNextScanner(countdown, values == null)));
532   }
533 
534   /**
535    * @param remainingResultSize
536    * @param remainingRows
537    * @param regionHasMoreResults
538    * @return true when the current region has been exhausted. When the current region has been
539    *         exhausted, the region must be changed before scanning can continue
540    */
541   private boolean doneWithRegion(long remainingResultSize, int remainingRows,
542       boolean regionHasMoreResults) {
543     return remainingResultSize > 0 && remainingRows > 0 && !regionHasMoreResults;
544   }
545 
546   /**
547    * This method ensures all of our book keeping regarding partial results is kept up to date. This
548    * method should be called once we know that the results we received back from the RPC request do
549    * not contain errors. We return a list of results that should be added to the cache. In general,
550    * this list will contain all NON-partial results from the input array (unless the client has
551    * specified that they are okay with receiving partial results)
552    * @param resultsFromServer The array of {@link Result}s returned from the server
553    * @param heartbeatMessage Flag indicating whether or not the response received from the server
554    *          represented a complete response, or a heartbeat message that was sent to keep the
555    *          client-server connection alive
556    * @return the list of results that should be added to the cache.
557    * @throws IOException
558    */
559   protected List<Result>
560       getResultsToAddToCache(Result[] resultsFromServer, boolean heartbeatMessage)
561           throws IOException {
562     int resultSize = resultsFromServer != null ? resultsFromServer.length : 0;
563     List<Result> resultsToAddToCache = new ArrayList<Result>(resultSize);
564 
565     final boolean isBatchSet = scan != null && scan.getBatch() > 0;
566     final boolean allowPartials = scan != null && scan.getAllowPartialResults();
567 
568     // If the caller has indicated in their scan that they are okay with seeing partial results,
569     // then simply add all results to the list. Note that since scan batching also returns results
570     // for a row in pieces we treat batch being set as equivalent to allowing partials. The
571     // implication of treating batching as equivalent to partial results is that it is possible
572     // the caller will receive a result back where the number of cells in the result is less than
573     // the batch size even though it may not be the last group of cells for that row.
574     if (allowPartials || isBatchSet) {
575       addResultsToList(resultsToAddToCache, resultsFromServer, 0, resultsFromServer.length);
576       return resultsToAddToCache;
577     }
578 
579     // If no results were returned it indicates that either we have the all the partial results
580     // necessary to construct the complete result or the server had to send a heartbeat message
581     // to the client to keep the client-server connection alive
582     if (resultsFromServer == null || resultsFromServer.length == 0) {
583       // If this response was an empty heartbeat message, then we have not exhausted the region
584       // and thus there may be more partials server side that still need to be added to the partial
585       // list before we form the complete Result
586       if (!partialResults.isEmpty() && !heartbeatMessage) {
587         resultsToAddToCache.add(Result.createCompleteResult(partialResults));
588         clearPartialResults();
589       }
590 
591       return resultsToAddToCache;
592     }
593 
594     // In every RPC response there should be at most a single partial result. Furthermore, if
595     // there is a partial result, it is guaranteed to be in the last position of the array.
596     Result last = resultsFromServer[resultsFromServer.length - 1];
597     Result partial = last.isPartial() ? last : null;
598 
599     if (LOG.isTraceEnabled()) {
600       StringBuilder sb = new StringBuilder();
601       sb.append("number results from RPC: ").append(resultsFromServer.length).append(",");
602       sb.append("partial != null: ").append(partial != null).append(",");
603       sb.append("number of partials so far: ").append(partialResults.size());
604       LOG.trace(sb.toString());
605     }
606 
607     // There are three possibilities cases that can occur while handling partial results
608     //
609     // 1. (partial != null && partialResults.isEmpty())
610     // This is the first partial result that we have received. It should be added to
611     // the list of partialResults and await the next RPC request at which point another
612     // portion of the complete result will be received
613     //
614     // 2. !partialResults.isEmpty()
615     // Since our partialResults list is not empty it means that we have been accumulating partial
616     // Results for a particular row. We cannot form the complete/whole Result for that row until
617     // all partials for the row have been received. Thus we loop through all of the Results
618     // returned from the server and determine whether or not all partial Results for the row have
619     // been received. We know that we have received all of the partial Results for the row when:
620     // i) We notice a row change in the Results
621     // ii) We see a Result for the partial row that is NOT marked as a partial Result
622     //
623     // 3. (partial == null && partialResults.isEmpty())
624     // Business as usual. We are not accumulating partial results and there wasn't a partial result
625     // in the RPC response. This means that all of the results we received from the server are
626     // complete and can be added directly to the cache
627     if (partial != null && partialResults.isEmpty()) {
628       addToPartialResults(partial);
629 
630       // Exclude the last result, it's a partial
631       addResultsToList(resultsToAddToCache, resultsFromServer, 0, resultsFromServer.length - 1);
632     } else if (!partialResults.isEmpty()) {
633       for (int i = 0; i < resultsFromServer.length; i++) {
634         Result result = resultsFromServer[i];
635 
636         // This result is from the same row as the partial Results. Add it to the list of partials
637         // and check if it was the last partial Result for that row
638         if (Bytes.equals(partialResultsRow, result.getRow())) {
639           addToPartialResults(result);
640 
641           // If the result is not a partial, it is a signal to us that it is the last Result we
642           // need to form the complete Result client-side
643           if (!result.isPartial()) {
644             resultsToAddToCache.add(Result.createCompleteResult(partialResults));
645             clearPartialResults();
646           }
647         } else {
648           // The row of this result differs from the row of the partial results we have received so
649           // far. If our list of partials isn't empty, this is a signal to form the complete Result
650           // since the row has now changed
651           if (!partialResults.isEmpty()) {
652             resultsToAddToCache.add(Result.createCompleteResult(partialResults));
653             clearPartialResults();
654           }
655 
656           // It's possible that in one response from the server we receive the final partial for
657           // one row and receive a partial for a different row. Thus, make sure that all Results
658           // are added to the proper list
659           if (result.isPartial()) {
660             addToPartialResults(result);
661           } else {
662             resultsToAddToCache.add(result);
663           }
664         }
665       }
666     } else { // partial == null && partialResults.isEmpty() -- business as usual
667       addResultsToList(resultsToAddToCache, resultsFromServer, 0, resultsFromServer.length);
668     }
669 
670     return resultsToAddToCache;
671   }
672 
673   /**
674    * A convenience method for adding a Result to our list of partials. This method ensure that only
675    * Results that belong to the same row as the other partials can be added to the list.
676    * @param result The result that we want to add to our list of partial Results
677    * @throws IOException
678    */
679   private void addToPartialResults(final Result result) throws IOException {
680     final byte[] row = result.getRow();
681     if (partialResultsRow != null && !Bytes.equals(row, partialResultsRow)) {
682       throw new IOException("Partial result row does not match. All partial results must come "
683           + "from the same row. partialResultsRow: " + Bytes.toString(partialResultsRow) + "row: "
684           + Bytes.toString(row));
685     }
686     partialResultsRow = row;
687     partialResults.add(result);
688   }
689 
690   /**
691    * Convenience method for clearing the list of partials and resetting the partialResultsRow.
692    */
693   private void clearPartialResults() {
694     partialResults.clear();
695     partialResultsRow = null;
696   }
697 
698   /**
699    * Helper method for adding results between the indices [start, end) to the outputList
700    * @param outputList the list that results will be added to
701    * @param inputArray the array that results are taken from
702    * @param start beginning index (inclusive)
703    * @param end ending index (exclusive)
704    */
705   private void addResultsToList(List<Result> outputList, Result[] inputArray, int start, int end) {
706     if (inputArray == null || start < 0 || end > inputArray.length) return;
707 
708     for (int i = start; i < end; i++) {
709       outputList.add(inputArray[i]);
710     }
711   }
712 
713     @Override
714     public void close() {
715       if (!scanMetricsPublished) writeScanMetrics();
716       if (callable != null) {
717         callable.setClose();
718         try {
719           call(callable, caller, scannerTimeout);
720         } catch (UnknownScannerException e) {
721            // We used to catch this error, interpret, and rethrow. However, we
722            // have since decided that it's not nice for a scanner's close to
723            // throw exceptions. Chances are it was just due to lease time out.
724           if (LOG.isDebugEnabled()) {
725             LOG.debug("scanner failed to close", e);
726           }
727         } catch (IOException e) {
728           /* An exception other than UnknownScanner is unexpected. */
729           LOG.warn("scanner failed to close.", e);
730         }
731         callable = null;
732       }
733       closed = true;
734     }
735 
736   /**
737    * Create the closest row before the specified row
738    * @param row
739    * @return a new byte array which is the closest front row of the specified one
740    */
741   protected static byte[] createClosestRowBefore(byte[] row) {
742     if (row == null) {
743       throw new IllegalArgumentException("The passed row is empty");
744     }
745     if (Bytes.equals(row, HConstants.EMPTY_BYTE_ARRAY)) {
746       return MAX_BYTE_ARRAY;
747     }
748     if (row[row.length - 1] == 0) {
749       return Arrays.copyOf(row, row.length - 1);
750     } else {
751       byte[] closestFrontRow = Arrays.copyOf(row, row.length);
752       closestFrontRow[row.length - 1] = (byte) ((closestFrontRow[row.length - 1] & 0xff) - 1);
753       closestFrontRow = Bytes.add(closestFrontRow, MAX_BYTE_ARRAY);
754       return closestFrontRow;
755     }
756   }
757 }