View Javadoc

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.KeyValue;
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 KeyValue.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                   int compare = Bytes.compareTo(o1.getFirst(), o2.getFirst());
192                   if (!isReversed()) {
193                     return compare;
194                   } else {
195                     return -compare;
196                   }
197                 }
198               });
199     }
200 
201     byte[] nextRow() {
202       if (nextRows.isEmpty()) {
203         throw new IllegalStateException(
204             "NextRows should not be empty, make sure to call nextRow() after updateTracker() return true");
205       } else {
206         return nextRows.peek().getFirst();
207       }
208     }
209 
210     boolean updateTracker(Cell currentCell) {
211       if (!initialized) {
212         for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
213           updateWith(currentCell, fuzzyData);
214         }
215         initialized = true;
216       } else {
217         while (!nextRows.isEmpty() && !lessThan(currentCell, nextRows.peek().getFirst())) {
218           Pair<byte[], Pair<byte[], byte[]>> head = nextRows.poll();
219           Pair<byte[], byte[]> fuzzyData = head.getSecond();
220           updateWith(currentCell, fuzzyData);
221         }
222       }
223       return !nextRows.isEmpty();
224     }
225 
226     boolean lessThan(Cell currentCell, byte[] nextRowKey) {
227       int compareResult =
228           Bytes.compareTo(currentCell.getRowArray(), currentCell.getRowOffset(),
229             currentCell.getRowLength(), nextRowKey, 0, nextRowKey.length);
230       return (!isReversed() && compareResult < 0) || (isReversed() && compareResult > 0);
231     }
232 
233     void updateWith(Cell currentCell, Pair<byte[], byte[]> fuzzyData) {
234       byte[] nextRowKeyCandidate =
235           getNextForFuzzyRule(isReversed(), currentCell.getRowArray(), currentCell.getRowOffset(),
236             currentCell.getRowLength(), fuzzyData.getFirst(), fuzzyData.getSecond());
237       if (nextRowKeyCandidate != null) {
238         nextRows.add(new Pair<byte[], Pair<byte[], byte[]>>(nextRowKeyCandidate, fuzzyData));
239       }
240     }
241 
242   }
243 
244   @Override
245   public boolean filterAllRemaining() {
246     return done;
247   }
248 
249   /**
250    * @return The filter serialized using pb
251    */
252   public byte[] toByteArray() {
253     FilterProtos.FuzzyRowFilter.Builder builder = FilterProtos.FuzzyRowFilter.newBuilder();
254     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
255       BytesBytesPair.Builder bbpBuilder = BytesBytesPair.newBuilder();
256       bbpBuilder.setFirst(ByteStringer.wrap(fuzzyData.getFirst()));
257       bbpBuilder.setSecond(ByteStringer.wrap(fuzzyData.getSecond()));
258       builder.addFuzzyKeysData(bbpBuilder);
259     }
260     return builder.build().toByteArray();
261   }
262 
263   /**
264    * @param pbBytes A pb serialized {@link FuzzyRowFilter} instance
265    * @return An instance of {@link FuzzyRowFilter} made from <code>bytes</code>
266    * @throws DeserializationException
267    * @see #toByteArray
268    */
269   public static FuzzyRowFilter parseFrom(final byte[] pbBytes) throws DeserializationException {
270     FilterProtos.FuzzyRowFilter proto;
271     try {
272       proto = FilterProtos.FuzzyRowFilter.parseFrom(pbBytes);
273     } catch (InvalidProtocolBufferException e) {
274       throw new DeserializationException(e);
275     }
276     int count = proto.getFuzzyKeysDataCount();
277     ArrayList<Pair<byte[], byte[]>> fuzzyKeysData = new ArrayList<Pair<byte[], byte[]>>(count);
278     for (int i = 0; i < count; ++i) {
279       BytesBytesPair current = proto.getFuzzyKeysData(i);
280       byte[] keyBytes = current.getFirst().toByteArray();
281       byte[] keyMeta = current.getSecond().toByteArray();
282       fuzzyKeysData.add(new Pair<byte[], byte[]>(keyBytes, keyMeta));
283     }
284     return new FuzzyRowFilter(fuzzyKeysData);
285   }
286 
287   @Override
288   public String toString() {
289     final StringBuilder sb = new StringBuilder();
290     sb.append("FuzzyRowFilter");
291     sb.append("{fuzzyKeysData=");
292     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
293       sb.append('{').append(Bytes.toStringBinary(fuzzyData.getFirst())).append(":");
294       sb.append(Bytes.toStringBinary(fuzzyData.getSecond())).append('}');
295     }
296     sb.append("}, ");
297     return sb.toString();
298   }
299 
300   // Utility methods
301 
302   static enum SatisfiesCode {
303     /** row satisfies fuzzy rule */
304     YES,
305     /** row doesn't satisfy fuzzy rule, but there's possible greater row that does */
306     NEXT_EXISTS,
307     /** row doesn't satisfy fuzzy rule and there's no greater row that does */
308     NO_NEXT
309   }
310 
311   @VisibleForTesting
312   static SatisfiesCode satisfies(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
313     return satisfies(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
314   }
315 
316   @VisibleForTesting
317   static SatisfiesCode satisfies(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
318       byte[] fuzzyKeyMeta) {
319     return satisfies(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
320   }
321 
322   static SatisfiesCode satisfies(boolean reverse, byte[] row, int offset, int length,
323       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
324 
325     if (!UNSAFE_UNALIGNED) {
326       return satisfiesNoUnsafe(reverse, row, offset, length, fuzzyKeyBytes, fuzzyKeyMeta);
327     }
328 
329     if (row == null) {
330       // do nothing, let scan to proceed
331       return SatisfiesCode.YES;
332     }
333     length = Math.min(length, fuzzyKeyBytes.length);
334     int numWords = length / Bytes.SIZEOF_LONG;
335     int offsetAdj = offset + UnsafeAccess.BYTE_ARRAY_BASE_OFFSET;
336 
337     int j = numWords << 3; // numWords * SIZEOF_LONG;
338 
339     for (int i = 0; i < j; i += Bytes.SIZEOF_LONG) {
340 
341       long fuzzyBytes =
342           UnsafeAccess.theUnsafe.getLong(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
343               + (long) i);
344       long fuzzyMeta =
345           UnsafeAccess.theUnsafe.getLong(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
346               + (long) i);
347       long rowValue = UnsafeAccess.theUnsafe.getLong(row, offsetAdj + (long) i);
348       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
349         // We always return NEXT_EXISTS
350         return SatisfiesCode.NEXT_EXISTS;
351       }
352     }
353 
354     int off = j;
355 
356     if (length - off >= Bytes.SIZEOF_INT) {
357       int fuzzyBytes =
358           UnsafeAccess.theUnsafe.getInt(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
359               + (long) off);
360       int fuzzyMeta =
361           UnsafeAccess.theUnsafe.getInt(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
362               + (long) off);
363       int rowValue = UnsafeAccess.theUnsafe.getInt(row, offsetAdj + (long) off);
364       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
365         // We always return NEXT_EXISTS
366         return SatisfiesCode.NEXT_EXISTS;
367       }
368       off += Bytes.SIZEOF_INT;
369     }
370 
371     if (length - off >= Bytes.SIZEOF_SHORT) {
372       short fuzzyBytes =
373           UnsafeAccess.theUnsafe.getShort(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
374               + (long) off);
375       short fuzzyMeta =
376           UnsafeAccess.theUnsafe.getShort(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
377               + (long) off);
378       short rowValue = UnsafeAccess.theUnsafe.getShort(row, offsetAdj + (long) off);
379       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
380         // We always return NEXT_EXISTS
381         // even if it does not (in this case getNextForFuzzyRule
382         // will return null)
383         return SatisfiesCode.NEXT_EXISTS;
384       }
385       off += Bytes.SIZEOF_SHORT;
386     }
387 
388     if (length - off >= Bytes.SIZEOF_BYTE) {
389       int fuzzyBytes = fuzzyKeyBytes[off] & 0xff;
390       int fuzzyMeta = fuzzyKeyMeta[off] & 0xff;
391       int rowValue = row[offset + off] & 0xff;
392       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
393         // We always return NEXT_EXISTS
394         return SatisfiesCode.NEXT_EXISTS;
395       }
396     }
397     return SatisfiesCode.YES;
398   }
399 
400   static SatisfiesCode satisfiesNoUnsafe(boolean reverse, byte[] row, int offset, int length,
401       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
402     if (row == null) {
403       // do nothing, let scan to proceed
404       return SatisfiesCode.YES;
405     }
406 
407     Order order = Order.orderFor(reverse);
408     boolean nextRowKeyCandidateExists = false;
409 
410     for (int i = 0; i < fuzzyKeyMeta.length && i < length; i++) {
411       // First, checking if this position is fixed and not equals the given one
412       boolean byteAtPositionFixed = fuzzyKeyMeta[i] == 0;
413       boolean fixedByteIncorrect = byteAtPositionFixed && fuzzyKeyBytes[i] != row[i + offset];
414       if (fixedByteIncorrect) {
415         // in this case there's another row that satisfies fuzzy rule and bigger than this row
416         if (nextRowKeyCandidateExists) {
417           return SatisfiesCode.NEXT_EXISTS;
418         }
419 
420         // If this row byte is less than fixed then there's a byte array bigger than
421         // this row and which satisfies the fuzzy rule. Otherwise there's no such byte array:
422         // this row is simply bigger than any byte array that satisfies the fuzzy rule
423         boolean rowByteLessThanFixed = (row[i + offset] & 0xFF) < (fuzzyKeyBytes[i] & 0xFF);
424         if (rowByteLessThanFixed && !reverse) {
425           return SatisfiesCode.NEXT_EXISTS;
426         } else if (!rowByteLessThanFixed && reverse) {
427           return SatisfiesCode.NEXT_EXISTS;
428         } else {
429           return SatisfiesCode.NO_NEXT;
430         }
431       }
432 
433       // Second, checking if this position is not fixed and byte value is not the biggest. In this
434       // case there's a byte array bigger than this row and which satisfies the fuzzy rule. To get
435       // bigger byte array that satisfies the rule we need to just increase this byte
436       // (see the code of getNextForFuzzyRule below) by one.
437       // Note: if non-fixed byte is already at biggest value, this doesn't allow us to say there's
438       // bigger one that satisfies the rule as it can't be increased.
439       if (fuzzyKeyMeta[i] == 1 && !order.isMax(fuzzyKeyBytes[i])) {
440         nextRowKeyCandidateExists = true;
441       }
442     }
443     return SatisfiesCode.YES;
444   }
445 
446   @VisibleForTesting
447   static byte[] getNextForFuzzyRule(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
448     return getNextForFuzzyRule(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
449   }
450 
451   @VisibleForTesting
452   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
453       byte[] fuzzyKeyMeta) {
454     return getNextForFuzzyRule(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
455   }
456 
457   /** Abstracts directional comparisons based on scan direction. */
458   private enum Order {
459     ASC {
460       public boolean lt(int lhs, int rhs) {
461         return lhs < rhs;
462       }
463 
464       public boolean gt(int lhs, int rhs) {
465         return lhs > rhs;
466       }
467 
468       public byte inc(byte val) {
469         // TODO: what about over/underflow?
470         return (byte) (val + 1);
471       }
472 
473       public boolean isMax(byte val) {
474         return val == (byte) 0xff;
475       }
476 
477       public byte min() {
478         return 0;
479       }
480     },
481     DESC {
482       public boolean lt(int lhs, int rhs) {
483         return lhs > rhs;
484       }
485 
486       public boolean gt(int lhs, int rhs) {
487         return lhs < rhs;
488       }
489 
490       public byte inc(byte val) {
491         // TODO: what about over/underflow?
492         return (byte) (val - 1);
493       }
494 
495       public boolean isMax(byte val) {
496         return val == 0;
497       }
498 
499       public byte min() {
500         return (byte) 0xFF;
501       }
502     };
503 
504     public static Order orderFor(boolean reverse) {
505       return reverse ? DESC : ASC;
506     }
507 
508     /** Returns true when {@code lhs < rhs}. */
509     public abstract boolean lt(int lhs, int rhs);
510 
511     /** Returns true when {@code lhs > rhs}. */
512     public abstract boolean gt(int lhs, int rhs);
513 
514     /** Returns {@code val} incremented by 1. */
515     public abstract byte inc(byte val);
516 
517     /** Return true when {@code val} is the maximum value */
518     public abstract boolean isMax(byte val);
519 
520     /** Return the minimum value according to this ordering scheme. */
521     public abstract byte min();
522   }
523 
524   /**
525    * @return greater byte array than given (row) which satisfies the fuzzy rule if it exists, null
526    *         otherwise
527    */
528   @VisibleForTesting
529   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, int offset, int length,
530       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
531     // To find out the next "smallest" byte array that satisfies fuzzy rule and "greater" than
532     // the given one we do the following:
533     // 1. setting values on all "fixed" positions to the values from fuzzyKeyBytes
534     // 2. if during the first step given row did not increase, then we increase the value at
535     // the first "non-fixed" position (where it is not maximum already)
536 
537     // It is easier to perform this by using fuzzyKeyBytes copy and setting "non-fixed" position
538     // values than otherwise.
539     byte[] result =
540         Arrays.copyOf(fuzzyKeyBytes, length > fuzzyKeyBytes.length ? length : fuzzyKeyBytes.length);
541     if (reverse && length > fuzzyKeyBytes.length) {
542       // we need trailing 0xff's instead of trailing 0x00's
543       for (int i = fuzzyKeyBytes.length; i < result.length; i++) {
544         result[i] = (byte) 0xFF;
545       }
546     }
547     int toInc = -1;
548     final Order order = Order.orderFor(reverse);
549 
550     boolean increased = false;
551     for (int i = 0; i < result.length; i++) {
552       if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
553         result[i] = row[offset + i];
554         if (!order.isMax(row[offset + i])) {
555           // this is "non-fixed" position and is not at max value, hence we can increase it
556           toInc = i;
557         }
558       } else if (i < fuzzyKeyMeta.length && fuzzyKeyMeta[i] == -1 /* fixed */) {
559         if (order.lt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
560           // if setting value for any fixed position increased the original array,
561           // we are OK
562           increased = true;
563           break;
564         }
565 
566         if (order.gt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
567           // if setting value for any fixed position makes array "smaller", then just stop:
568           // in case we found some non-fixed position to increase we will do it, otherwise
569           // there's no "next" row key that satisfies fuzzy rule and "greater" than given row
570           break;
571         }
572       }
573     }
574 
575     if (!increased) {
576       if (toInc < 0) {
577         return null;
578       }
579       result[toInc] = order.inc(result[toInc]);
580 
581       // Setting all "non-fixed" positions to zeroes to the right of the one we increased so
582       // that found "next" row key is the smallest possible
583       for (int i = toInc + 1; i < result.length; i++) {
584         if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
585           result[i] = order.min();
586         }
587       }
588     }
589 
590     return reverse? result: trimTrailingZeroes(result, fuzzyKeyMeta, toInc);
591   }
592 
593   /**
594    * For forward scanner, next cell hint should  not contain any trailing zeroes
595    * unless they are part of fuzzyKeyMeta
596    * hint = '\x01\x01\x01\x00\x00'
597    * will skip valid row '\x01\x01\x01'
598    * 
599    * @param result
600    * @param fuzzyKeyMeta
601    * @param toInc - position of incremented byte
602    * @return trimmed version of result
603    */
604   
605   private static byte[] trimTrailingZeroes(byte[] result, byte[] fuzzyKeyMeta, int toInc) {
606     int off = fuzzyKeyMeta.length >= result.length? result.length -1:
607            fuzzyKeyMeta.length -1;  
608     for( ; off >= 0; off--){
609       if(fuzzyKeyMeta[off] != 0) break;
610     }
611     if (off < toInc)  off = toInc;
612     byte[] retValue = new byte[off+1];
613     System.arraycopy(result, 0, retValue, 0, retValue.length);
614     return retValue;
615   }
616 
617   /**
618    * @return true if and only if the fields of the filter that are serialized are equal to the
619    *         corresponding fields in other. Used for testing.
620    */
621   boolean areSerializedFieldsEqual(Filter o) {
622     if (o == this) return true;
623     if (!(o instanceof FuzzyRowFilter)) return false;
624 
625     FuzzyRowFilter other = (FuzzyRowFilter) o;
626     if (this.fuzzyKeysData.size() != other.fuzzyKeysData.size()) return false;
627     for (int i = 0; i < fuzzyKeysData.size(); ++i) {
628       Pair<byte[], byte[]> thisData = this.fuzzyKeysData.get(i);
629       Pair<byte[], byte[]> otherData = other.fuzzyKeysData.get(i);
630       if (!(Bytes.equals(thisData.getFirst(), otherData.getFirst()) && Bytes.equals(
631         thisData.getSecond(), otherData.getSecond()))) {
632         return false;
633       }
634     }
635     return true;
636   }
637 }