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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.filter;
19  
20  import java.util.ArrayList;
21  import java.util.Arrays;
22  import java.util.Comparator;
23  import java.util.List;
24  import java.util.PriorityQueue;
25  
26  import org.apache.hadoop.hbase.Cell;
27  import org.apache.hadoop.hbase.KeyValueUtil;
28  import org.apache.hadoop.hbase.classification.InterfaceAudience;
29  import org.apache.hadoop.hbase.classification.InterfaceStability;
30  import org.apache.hadoop.hbase.exceptions.DeserializationException;
31  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
32  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.BytesBytesPair;
33  import org.apache.hadoop.hbase.util.ByteStringer;
34  import org.apache.hadoop.hbase.util.Bytes;
35  import org.apache.hadoop.hbase.util.Pair;
36  import org.apache.hadoop.hbase.util.UnsafeAccess;
37  import org.apache.hadoop.hbase.util.UnsafeAvailChecker;
38  
39  import com.google.common.annotations.VisibleForTesting;
40  import com.google.protobuf.InvalidProtocolBufferException;
41  
42  /**
43   * This is optimized version of a standard FuzzyRowFilter Filters data based on fuzzy row key.
44   * Performs fast-forwards during scanning. It takes pairs (row key, fuzzy info) to match row keys.
45   * Where fuzzy info is a byte array with 0 or 1 as its values:
46   * <ul>
47   * <li>0 - means that this byte in provided row key is fixed, i.e. row key's byte at same position
48   * must match</li>
49   * <li>1 - means that this byte in provided row key is NOT fixed, i.e. row key's byte at this
50   * position can be different from the one in provided row key</li>
51   * </ul>
52   * Example: Let's assume row key format is userId_actionId_year_month. Length of userId is fixed and
53   * is 4, length of actionId is 2 and year and month are 4 and 2 bytes long respectively. Let's
54   * assume that we need to fetch all users that performed certain action (encoded as "99") in Jan of
55   * any year. Then the pair (row key, fuzzy info) would be the following: row key = "????_99_????_01"
56   * (one can use any value instead of "?") fuzzy info =
57   * "\x01\x01\x01\x01\x00\x00\x00\x00\x01\x01\x01\x01\x00\x00\x00" I.e. fuzzy info tells the matching
58   * mask is "????_99_????_01", where at ? can be any value.
59   */
60  @InterfaceAudience.Public
61  @InterfaceStability.Evolving
62  public class FuzzyRowFilter extends FilterBase {
63    private static final boolean UNSAFE_UNALIGNED = UnsafeAvailChecker.unaligned();
64    private List<Pair<byte[], byte[]>> fuzzyKeysData;
65    private boolean done = false;
66  
67    /**
68     * The index of a last successfully found matching fuzzy string (in fuzzyKeysData). We will start
69     * matching next KV with this one. If they do not match then we will return back to the one-by-one
70     * iteration over fuzzyKeysData.
71     */
72    private int lastFoundIndex = -1;
73  
74    /**
75     * Row tracker (keeps all next rows after SEEK_NEXT_USING_HINT was returned)
76     */
77    private RowTracker tracker;
78  
79    public FuzzyRowFilter(List<Pair<byte[], byte[]>> fuzzyKeysData) {
80      Pair<byte[], byte[]> p;
81      for (int i = 0; i < fuzzyKeysData.size(); i++) {
82        p = fuzzyKeysData.get(i);
83        if (p.getFirst().length != p.getSecond().length) {
84          Pair<String, String> readable =
85              new Pair<String, String>(Bytes.toStringBinary(p.getFirst()), Bytes.toStringBinary(p
86                  .getSecond()));
87          throw new IllegalArgumentException("Fuzzy pair lengths do not match: " + readable);
88        }
89        // update mask ( 0 -> -1 (0xff), 1 -> 0)
90        p.setSecond(preprocessMask(p.getSecond()));
91        preprocessSearchKey(p);
92      }
93      this.fuzzyKeysData = fuzzyKeysData;
94      this.tracker = new RowTracker();
95    }
96  
97    private void preprocessSearchKey(Pair<byte[], byte[]> p) {
98      if (!UNSAFE_UNALIGNED) {
99        return;
100     }
101     byte[] key = p.getFirst();
102     byte[] mask = p.getSecond();
103     for (int i = 0; i < mask.length; i++) {
104       // set non-fixed part of a search key to 0.
105       if (mask[i] == 0) key[i] = 0;
106     }
107   }
108 
109   /**
110    * We need to preprocess mask array, as since we treat 0's as unfixed positions and -1 (0xff) as
111    * fixed positions
112    * @param mask
113    * @return mask array
114    */
115   private byte[] preprocessMask(byte[] mask) {
116     if (!UNSAFE_UNALIGNED) {
117       return mask;
118     }
119     if (isPreprocessedMask(mask)) return mask;
120     for (int i = 0; i < mask.length; i++) {
121       if (mask[i] == 0) {
122         mask[i] = -1; // 0 -> -1
123       } else if (mask[i] == 1) {
124         mask[i] = 0;// 1 -> 0
125       }
126     }
127     return mask;
128   }
129 
130   private boolean isPreprocessedMask(byte[] mask) {
131     for (int i = 0; i < mask.length; i++) {
132       if (mask[i] != -1 && mask[i] != 0) {
133         return false;
134       }
135     }
136     return true;
137   }
138 
139   @Override
140   public ReturnCode filterKeyValue(Cell c) {
141     final int startIndex = lastFoundIndex >= 0 ? lastFoundIndex : 0;
142     final int size = fuzzyKeysData.size();
143     for (int i = startIndex; i < size + startIndex; i++) {
144       final int index = i % size;
145       Pair<byte[], byte[]> fuzzyData = fuzzyKeysData.get(index);
146       SatisfiesCode satisfiesCode =
147           satisfies(isReversed(), c.getRowArray(), c.getRowOffset(), c.getRowLength(),
148             fuzzyData.getFirst(), fuzzyData.getSecond());
149       if (satisfiesCode == SatisfiesCode.YES) {
150         lastFoundIndex = index;
151         return ReturnCode.INCLUDE;
152       }
153     }
154     // NOT FOUND -> seek next using hint
155     lastFoundIndex = -1;
156 
157     return ReturnCode.SEEK_NEXT_USING_HINT;
158 
159   }
160 
161   @Override
162   public Cell getNextCellHint(Cell currentCell) {
163     boolean result = tracker.updateTracker(currentCell);
164     if (result == false) {
165       done = true;
166       return null;
167     }
168     byte[] nextRowKey = tracker.nextRow();
169     return KeyValueUtil.createFirstOnRow(nextRowKey);
170   }
171 
172   /**
173    * If we have multiple fuzzy keys, row tracker should improve overall performance. It calculates
174    * all next rows (one per every fuzzy key) and put them (the fuzzy key is bundled) into a priority
175    * queue so that the smallest row key always appears at queue head, which helps to decide the
176    * "Next Cell Hint". As scanning going on, the number of candidate rows in the RowTracker will
177    * remain the size of fuzzy keys until some of the fuzzy keys won't possibly have matches any
178    * more.
179    */
180   private class RowTracker {
181     private final PriorityQueue<Pair<byte[], Pair<byte[], byte[]>>> nextRows;
182     private boolean initialized = false;
183 
184     RowTracker() {
185       nextRows =
186           new PriorityQueue<Pair<byte[], Pair<byte[], byte[]>>>(fuzzyKeysData.size(),
187               new Comparator<Pair<byte[], Pair<byte[], byte[]>>>() {
188                 @Override
189                 public int compare(Pair<byte[], Pair<byte[], byte[]>> o1,
190                     Pair<byte[], Pair<byte[], byte[]>> o2) {
191                   return isReversed()? Bytes.compareTo(o2.getFirst(), o1.getFirst()):
192                     Bytes.compareTo(o1.getFirst(), o2.getFirst());
193                 }
194               });
195     }
196 
197     byte[] nextRow() {
198       if (nextRows.isEmpty()) {
199         throw new IllegalStateException(
200             "NextRows should not be empty, make sure to call nextRow() after updateTracker() return true");
201       } else {
202         return nextRows.peek().getFirst();
203       }
204     }
205 
206     boolean updateTracker(Cell currentCell) {
207       if (!initialized) {
208         for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
209           updateWith(currentCell, fuzzyData);
210         }
211         initialized = true;
212       } else {
213         while (!nextRows.isEmpty() && !lessThan(currentCell, nextRows.peek().getFirst())) {
214           Pair<byte[], Pair<byte[], byte[]>> head = nextRows.poll();
215           Pair<byte[], byte[]> fuzzyData = head.getSecond();
216           updateWith(currentCell, fuzzyData);
217         }
218       }
219       return !nextRows.isEmpty();
220     }
221 
222     boolean lessThan(Cell currentCell, byte[] nextRowKey) {
223       int compareResult =
224           Bytes.compareTo(currentCell.getRowArray(), currentCell.getRowOffset(),
225             currentCell.getRowLength(), nextRowKey, 0, nextRowKey.length);
226       return (!isReversed() && compareResult < 0) || (isReversed() && compareResult > 0);
227     }
228 
229     void updateWith(Cell currentCell, Pair<byte[], byte[]> fuzzyData) {
230       byte[] nextRowKeyCandidate =
231           getNextForFuzzyRule(isReversed(), currentCell.getRowArray(), currentCell.getRowOffset(),
232             currentCell.getRowLength(), fuzzyData.getFirst(), fuzzyData.getSecond());
233       if (nextRowKeyCandidate != null) {
234         nextRows.add(new Pair<byte[], Pair<byte[], byte[]>>(nextRowKeyCandidate, fuzzyData));
235       }
236     }
237 
238   }
239 
240   @Override
241   public boolean filterAllRemaining() {
242     return done;
243   }
244 
245   /**
246    * @return The filter serialized using pb
247    */
248   public byte[] toByteArray() {
249     FilterProtos.FuzzyRowFilter.Builder builder = FilterProtos.FuzzyRowFilter.newBuilder();
250     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
251       BytesBytesPair.Builder bbpBuilder = BytesBytesPair.newBuilder();
252       bbpBuilder.setFirst(ByteStringer.wrap(fuzzyData.getFirst()));
253       bbpBuilder.setSecond(ByteStringer.wrap(fuzzyData.getSecond()));
254       builder.addFuzzyKeysData(bbpBuilder);
255     }
256     return builder.build().toByteArray();
257   }
258 
259   /**
260    * @param pbBytes A pb serialized {@link FuzzyRowFilter} instance
261    * @return An instance of {@link FuzzyRowFilter} made from <code>bytes</code>
262    * @throws DeserializationException
263    * @see #toByteArray
264    */
265   public static FuzzyRowFilter parseFrom(final byte[] pbBytes) throws DeserializationException {
266     FilterProtos.FuzzyRowFilter proto;
267     try {
268       proto = FilterProtos.FuzzyRowFilter.parseFrom(pbBytes);
269     } catch (InvalidProtocolBufferException e) {
270       throw new DeserializationException(e);
271     }
272     int count = proto.getFuzzyKeysDataCount();
273     ArrayList<Pair<byte[], byte[]>> fuzzyKeysData = new ArrayList<Pair<byte[], byte[]>>(count);
274     for (int i = 0; i < count; ++i) {
275       BytesBytesPair current = proto.getFuzzyKeysData(i);
276       byte[] keyBytes = current.getFirst().toByteArray();
277       byte[] keyMeta = current.getSecond().toByteArray();
278       fuzzyKeysData.add(new Pair<byte[], byte[]>(keyBytes, keyMeta));
279     }
280     return new FuzzyRowFilter(fuzzyKeysData);
281   }
282 
283   @Override
284   public String toString() {
285     final StringBuilder sb = new StringBuilder();
286     sb.append("FuzzyRowFilter");
287     sb.append("{fuzzyKeysData=");
288     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
289       sb.append('{').append(Bytes.toStringBinary(fuzzyData.getFirst())).append(":");
290       sb.append(Bytes.toStringBinary(fuzzyData.getSecond())).append('}');
291     }
292     sb.append("}, ");
293     return sb.toString();
294   }
295 
296   // Utility methods
297 
298   static enum SatisfiesCode {
299     /** row satisfies fuzzy rule */
300     YES,
301     /** row doesn't satisfy fuzzy rule, but there's possible greater row that does */
302     NEXT_EXISTS,
303     /** row doesn't satisfy fuzzy rule and there's no greater row that does */
304     NO_NEXT
305   }
306 
307   @VisibleForTesting
308   static SatisfiesCode satisfies(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
309     return satisfies(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
310   }
311 
312   @VisibleForTesting
313   static SatisfiesCode satisfies(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
314       byte[] fuzzyKeyMeta) {
315     return satisfies(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
316   }
317 
318   static SatisfiesCode satisfies(boolean reverse, byte[] row, int offset, int length,
319       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
320 
321     if (!UNSAFE_UNALIGNED) {
322       return satisfiesNoUnsafe(reverse, row, offset, length, fuzzyKeyBytes, fuzzyKeyMeta);
323     }
324 
325     if (row == null) {
326       // do nothing, let scan to proceed
327       return SatisfiesCode.YES;
328     }
329     length = Math.min(length, fuzzyKeyBytes.length);
330     int numWords = length / Bytes.SIZEOF_LONG;
331     int offsetAdj = offset + UnsafeAccess.BYTE_ARRAY_BASE_OFFSET;
332 
333     int j = numWords << 3; // numWords * SIZEOF_LONG;
334 
335     for (int i = 0; i < j; i += Bytes.SIZEOF_LONG) {
336 
337       long fuzzyBytes =
338           UnsafeAccess.theUnsafe.getLong(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
339               + (long) i);
340       long fuzzyMeta =
341           UnsafeAccess.theUnsafe.getLong(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
342               + (long) i);
343       long rowValue = UnsafeAccess.theUnsafe.getLong(row, offsetAdj + (long) i);
344       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
345         // We always return NEXT_EXISTS
346         return SatisfiesCode.NEXT_EXISTS;
347       }
348     }
349 
350     int off = j;
351 
352     if (length - off >= Bytes.SIZEOF_INT) {
353       int fuzzyBytes =
354           UnsafeAccess.theUnsafe.getInt(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
355               + (long) off);
356       int fuzzyMeta =
357           UnsafeAccess.theUnsafe.getInt(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
358               + (long) off);
359       int rowValue = UnsafeAccess.theUnsafe.getInt(row, offsetAdj + (long) off);
360       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
361         // We always return NEXT_EXISTS
362         return SatisfiesCode.NEXT_EXISTS;
363       }
364       off += Bytes.SIZEOF_INT;
365     }
366 
367     if (length - off >= Bytes.SIZEOF_SHORT) {
368       short fuzzyBytes =
369           UnsafeAccess.theUnsafe.getShort(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
370               + (long) off);
371       short fuzzyMeta =
372           UnsafeAccess.theUnsafe.getShort(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
373               + (long) off);
374       short rowValue = UnsafeAccess.theUnsafe.getShort(row, offsetAdj + (long) off);
375       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
376         // We always return NEXT_EXISTS
377         // even if it does not (in this case getNextForFuzzyRule
378         // will return null)
379         return SatisfiesCode.NEXT_EXISTS;
380       }
381       off += Bytes.SIZEOF_SHORT;
382     }
383 
384     if (length - off >= Bytes.SIZEOF_BYTE) {
385       int fuzzyBytes = fuzzyKeyBytes[off] & 0xff;
386       int fuzzyMeta = fuzzyKeyMeta[off] & 0xff;
387       int rowValue = row[offset + off] & 0xff;
388       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
389         // We always return NEXT_EXISTS
390         return SatisfiesCode.NEXT_EXISTS;
391       }
392     }
393     return SatisfiesCode.YES;
394   }
395 
396   static SatisfiesCode satisfiesNoUnsafe(boolean reverse, byte[] row, int offset, int length,
397       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
398     if (row == null) {
399       // do nothing, let scan to proceed
400       return SatisfiesCode.YES;
401     }
402 
403     Order order = Order.orderFor(reverse);
404     boolean nextRowKeyCandidateExists = false;
405 
406     for (int i = 0; i < fuzzyKeyMeta.length && i < length; i++) {
407       // First, checking if this position is fixed and not equals the given one
408       boolean byteAtPositionFixed = fuzzyKeyMeta[i] == 0;
409       boolean fixedByteIncorrect = byteAtPositionFixed && fuzzyKeyBytes[i] != row[i + offset];
410       if (fixedByteIncorrect) {
411         // in this case there's another row that satisfies fuzzy rule and bigger than this row
412         if (nextRowKeyCandidateExists) {
413           return SatisfiesCode.NEXT_EXISTS;
414         }
415 
416         // If this row byte is less than fixed then there's a byte array bigger than
417         // this row and which satisfies the fuzzy rule. Otherwise there's no such byte array:
418         // this row is simply bigger than any byte array that satisfies the fuzzy rule
419         boolean rowByteLessThanFixed = (row[i + offset] & 0xFF) < (fuzzyKeyBytes[i] & 0xFF);
420         if (rowByteLessThanFixed && !reverse) {
421           return SatisfiesCode.NEXT_EXISTS;
422         } else if (!rowByteLessThanFixed && reverse) {
423           return SatisfiesCode.NEXT_EXISTS;
424         } else {
425           return SatisfiesCode.NO_NEXT;
426         }
427       }
428 
429       // Second, checking if this position is not fixed and byte value is not the biggest. In this
430       // case there's a byte array bigger than this row and which satisfies the fuzzy rule. To get
431       // bigger byte array that satisfies the rule we need to just increase this byte
432       // (see the code of getNextForFuzzyRule below) by one.
433       // Note: if non-fixed byte is already at biggest value, this doesn't allow us to say there's
434       // bigger one that satisfies the rule as it can't be increased.
435       if (fuzzyKeyMeta[i] == 1 && !order.isMax(fuzzyKeyBytes[i])) {
436         nextRowKeyCandidateExists = true;
437       }
438     }
439     return SatisfiesCode.YES;
440   }
441 
442   @VisibleForTesting
443   static byte[] getNextForFuzzyRule(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
444     return getNextForFuzzyRule(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
445   }
446 
447   @VisibleForTesting
448   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
449       byte[] fuzzyKeyMeta) {
450     return getNextForFuzzyRule(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
451   }
452 
453   /** Abstracts directional comparisons based on scan direction. */
454   private enum Order {
455     ASC {
456       public boolean lt(int lhs, int rhs) {
457         return lhs < rhs;
458       }
459 
460       public boolean gt(int lhs, int rhs) {
461         return lhs > rhs;
462       }
463 
464       public byte inc(byte val) {
465         // TODO: what about over/underflow?
466         return (byte) (val + 1);
467       }
468 
469       public boolean isMax(byte val) {
470         return val == (byte) 0xff;
471       }
472 
473       public byte min() {
474         return 0;
475       }
476     },
477     DESC {
478       public boolean lt(int lhs, int rhs) {
479         return lhs > rhs;
480       }
481 
482       public boolean gt(int lhs, int rhs) {
483         return lhs < rhs;
484       }
485 
486       public byte inc(byte val) {
487         // TODO: what about over/underflow?
488         return (byte) (val - 1);
489       }
490 
491       public boolean isMax(byte val) {
492         return val == 0;
493       }
494 
495       public byte min() {
496         return (byte) 0xFF;
497       }
498     };
499 
500     public static Order orderFor(boolean reverse) {
501       return reverse ? DESC : ASC;
502     }
503 
504     /** Returns true when {@code lhs < rhs}. */
505     public abstract boolean lt(int lhs, int rhs);
506 
507     /** Returns true when {@code lhs > rhs}. */
508     public abstract boolean gt(int lhs, int rhs);
509 
510     /** Returns {@code val} incremented by 1. */
511     public abstract byte inc(byte val);
512 
513     /** Return true when {@code val} is the maximum value */
514     public abstract boolean isMax(byte val);
515 
516     /** Return the minimum value according to this ordering scheme. */
517     public abstract byte min();
518   }
519 
520   /**
521    * @return greater byte array than given (row) which satisfies the fuzzy rule if it exists, null
522    *         otherwise
523    */
524   @VisibleForTesting
525   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, int offset, int length,
526       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
527     // To find out the next "smallest" byte array that satisfies fuzzy rule and "greater" than
528     // the given one we do the following:
529     // 1. setting values on all "fixed" positions to the values from fuzzyKeyBytes
530     // 2. if during the first step given row did not increase, then we increase the value at
531     // the first "non-fixed" position (where it is not maximum already)
532 
533     // It is easier to perform this by using fuzzyKeyBytes copy and setting "non-fixed" position
534     // values than otherwise.
535     byte[] result =
536         Arrays.copyOf(fuzzyKeyBytes, length > fuzzyKeyBytes.length ? length : fuzzyKeyBytes.length);
537     if (reverse && length > fuzzyKeyBytes.length) {
538       // we need trailing 0xff's instead of trailing 0x00's
539       for (int i = fuzzyKeyBytes.length; i < result.length; i++) {
540         result[i] = (byte) 0xFF;
541       }
542     }
543     int toInc = -1;
544     final Order order = Order.orderFor(reverse);
545 
546     boolean increased = false;
547     for (int i = 0; i < result.length; i++) {
548       if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
549         result[i] = row[offset + i];
550         if (!order.isMax(row[offset + i])) {
551           // this is "non-fixed" position and is not at max value, hence we can increase it
552           toInc = i;
553         }
554       } else if (i < fuzzyKeyMeta.length && fuzzyKeyMeta[i] == -1 /* fixed */) {
555         if (order.lt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
556           // if setting value for any fixed position increased the original array,
557           // we are OK
558           increased = true;
559           break;
560         }
561 
562         if (order.gt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
563           // if setting value for any fixed position makes array "smaller", then just stop:
564           // in case we found some non-fixed position to increase we will do it, otherwise
565           // there's no "next" row key that satisfies fuzzy rule and "greater" than given row
566           break;
567         }
568       }
569     }
570 
571     if (!increased) {
572       if (toInc < 0) {
573         return null;
574       }
575       result[toInc] = order.inc(result[toInc]);
576 
577       // Setting all "non-fixed" positions to zeroes to the right of the one we increased so
578       // that found "next" row key is the smallest possible
579       for (int i = toInc + 1; i < result.length; i++) {
580         if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
581           result[i] = order.min();
582         }
583       }
584     }
585 
586     return reverse? result: trimTrailingZeroes(result, fuzzyKeyMeta, toInc);
587   }
588 
589   /**
590    * For forward scanner, next cell hint should  not contain any trailing zeroes
591    * unless they are part of fuzzyKeyMeta
592    * hint = '\x01\x01\x01\x00\x00'
593    * will skip valid row '\x01\x01\x01'
594    * 
595    * @param result
596    * @param fuzzyKeyMeta
597    * @param toInc - position of incremented byte
598    * @return trimmed version of result
599    */
600   
601   private static byte[] trimTrailingZeroes(byte[] result, byte[] fuzzyKeyMeta, int toInc) {
602     int off = fuzzyKeyMeta.length >= result.length? result.length -1:
603            fuzzyKeyMeta.length -1;  
604     for( ; off >= 0; off--){
605       if(fuzzyKeyMeta[off] != 0) break;
606     }
607     if (off < toInc)  off = toInc;
608     byte[] retValue = new byte[off+1];
609     System.arraycopy(result, 0, retValue, 0, retValue.length);
610     return retValue;
611   }
612 
613   /**
614    * @return true if and only if the fields of the filter that are serialized are equal to the
615    *         corresponding fields in other. Used for testing.
616    */
617   boolean areSerializedFieldsEqual(Filter o) {
618     if (o == this) return true;
619     if (!(o instanceof FuzzyRowFilter)) return false;
620 
621     FuzzyRowFilter other = (FuzzyRowFilter) o;
622     if (this.fuzzyKeysData.size() != other.fuzzyKeysData.size()) return false;
623     for (int i = 0; i < fuzzyKeysData.size(); ++i) {
624       Pair<byte[], byte[]> thisData = this.fuzzyKeysData.get(i);
625       Pair<byte[], byte[]> otherData = other.fuzzyKeysData.get(i);
626       if (!(Bytes.equals(thisData.getFirst(), otherData.getFirst()) && Bytes.equals(
627         thisData.getSecond(), otherData.getSecond()))) {
628         return false;
629       }
630     }
631     return true;
632   }
633 }