I clean the code snippet:
When I work on PHOENIX-1193 to make skip scan work with reverse scan and read the code of SkipScanFilter.navigate method, it seems that SkipScanFilter.navigate method has a bug, please help me see if I am right. See following simple unit test first,the rowKey is composed of three PInteger columns,and the slots of SkipScanFilter are: [[[1 - 4]], [5, 7], [[9 - 10]]], when SkipScanFilter.filterKeyValue method is invoked on a KeyValue whose rowKey is [2,7,11], obviously SkipScanFilter.filterKeyValue returns ReturnCode.SEEK_NEXT_USING_HINT and SkipScanFilter.getNextCellHint returns [3,5,9], but unfortunately, SkipScanFilter.getNextCellHint actually returns [2,8,5,9] , a very strange value, following unit tests failed. Let us see what's wrong, first column of rowKey [2,7,11 ] is 2, which is in SkipScanFilter's first slot range [1-4], so position[0] is 0 and we go to the second column 7, which match the second range [7] of SkipScanFilter's second slot [5, 7],so position[1] is 1 and we go to the third column 11, which is bigger than the third slot range [9 - 10],so position[2] is 0 and we begin to backtrack to second column, because the second range [7] of SkipScanFilter's second slot is singleKey and there is no more range,so position[1] is 0 and we continue to backtrack to first column, because the first slot range [1-4] is not singleKey so we stop backtracking at first column. Now the problem comes, in following line 448 of SkipScanFilter.navigate method,SkipScanFilter.setStartKey method is invoked,first copy rowKey columns before ptr to SkipScanFilter.startKey, because now ptr still point to the third column, so copy the first and second columns to SkipScanFilter.startKey,SkipScanFilter.startKey is [2,7] after this step , then setStartKey method copy the lower bound SkipScanFilter.slots from j+1 column, accoring to SkipScanFilter.position array,now j is 0, and both position[1] and position[2] are 0,so SkipScanFilter.startKey becomes [2,7,5,9], and in following line 457, ByteUtil.nextKey is invoked on [2,7], [2,7] is incremented to [2,8], finally SkipScanFilter.startKey is [2,8,5,9]. From above analysis, we can see the second column is repeatedly copied to SkipScanFilter.startKey, copy 7 to SkipScanFilter.startKey is error ,before SkipScanFilter.setStartKey method is invoked in line 448, we should first move ptr to j+1, that is to say ,following code might be inserted before line 448: schema.reposition( ptr, ScanUtil.getRowKeyPosition(slotSpan, i), ScanUtil.getRowKeyPosition(slotSpan, j+1), minOffset, maxOffset, slotSpan[j+1]); Another problem is why the existing SkipScanFilter unit tests are ok? That is because in all existing unit test cases, backtrack column is just before current column which ptr points to, i.e. i==j+1, and this problem may not affect the final query result , but obviously, it may lead to the erroneous startKey and cause the Skip Scan inefficient. At 2017-02-28 19:31:50, "程磊" <[email protected]> wrote: >When I work on PHOENIX-1193 to make skip scan work with reverse scan and read >the code of SkipScanFilter.navigate method, it seems that >SkipScanFilter.navigate method has a bug, please help me see if I am right. > > >See following simple unit test first,the rowKey is composed of three PInteger >columns,and the slots of SkipScanFilter are: >[[[1 - 4]], [5, 7], [[9 - 10]]], >when SkipScanFilter.filterKeyValue method is invoked on a KeyValue whose >rowKey is [2,7,11], obviously SkipScanFilter.filterKeyValue >returns ReturnCode.SEEK_NEXT_USING_HINT and SkipScanFilter.getNextCellHint >returns [3,5,9], but unfortunately, SkipScanFilter.getNextCellHint actually >returns [2,8,5,9] , a very strange value, following unit tests failed. > > >@Test public void testNavigate() { RowKeySchemaBuilder builder = new >RowKeySchemaBuilder(3); for(int i=0;i<3;i++) { builder.addField( new PDatum() >{ @Override public boolean isNullable() { return false; } @Override public >PDataType getDataType() { return PInteger.INSTANCE; } @Override public Integer >getMaxLength() { return PInteger.INSTANCE.getMaxLength(null); } @Override >public Integer getScale() { return PInteger.INSTANCE.getScale(null); } >@Override public SortOrder getSortOrder() { return SortOrder.getDefault(); } >}, false, SortOrder.getDefault()); } List<List<KeyRange>> >rowKeyColumnRangesList=Arrays.asList( Arrays.asList( >PInteger.INSTANCE.getKeyRange(PInteger.INSTANCE.toBytes(1), true, >PInteger.INSTANCE.toBytes(4), true)), Arrays.asList( >KeyRange.getKeyRange(PInteger.INSTANCE.toBytes(5)), >KeyRange.getKeyRange(PInteger.INSTANCE.toBytes(7))), Arrays.asList( >PInteger.INSTANCE.getKeyRange(PInteger.INSTANCE.toBytes(9), true, >PInteger.INSTANCE.toBytes(10), true)) ); SkipScanFilter skipScanFilter=new >SkipScanFilter(rowKeyColumnRangesList, builder.build()); >System.out.println(skipScanFilter); byte[] rowKey=ByteUtil.concat( >PInteger.INSTANCE.toBytes(2), PInteger.INSTANCE.toBytes(7), >PInteger.INSTANCE.toBytes(11)); KeyValue >keyValue=KeyValue.createFirstOnRow(rowKey); ReturnCode >returnCode=skipScanFilter.filterKeyValue(keyValue); assertTrue(returnCode == >ReturnCode.SEEK_NEXT_USING_HINT); Cell >nextCellHint=skipScanFilter.getNextCellHint(keyValue); >assertTrue(Bytes.toStringBinary(CellUtil.cloneRow(nextCellHint)).equals("\\x80\\x00\\x00\\x03\\x80\\x00\\x00\\x05\\x80\\x00\\x00\\x09")); > } > > >Let us see what's wrong, first column of rowKey [2,7,11 ] is 2, which is in >SkipScanFilter's first slot range [1-4], so position[0] is 0 and we go to the >second column 7, which match the second range [7] of SkipScanFilter's second >slot [5, 7],so position[1] is 1 and we go to the third column 11, which is >bigger than the third slot range [9 - 10],so position[2] is 0 and we begin to >backtrack to second column, because the second range [7] of SkipScanFilter's >second slot is singleKey and there is no more range,so position[1] is 0 and we >continue to backtrack to first column, because the first slot range [1-4] is >not singleKey so we stop backtracking at first column. > > >Now the problem comes, in following line 448 of SkipScanFilter.navigate >method,SkipScanFilter.setStartKey method is invoked,first copy rowKey columns >before ptr to SkipScanFilter.startKey, because now ptr still point to the >third column, so copy the first and second columns to >SkipScanFilter.startKey,SkipScanFilter.startKey is [2,7] after this step , >then setStartKey method copy the lower bound SkipScanFilter.slots from j+1 >column, accoring to SkipScanFilter.position array,now j is 0, and both >position[1] and position[2] are 0,so SkipScanFilter.startKey becomes >[2,7,5,9], and in following line 457, ByteUtil.nextKey is invoked on [2,7], >[2,7] is incremented to [2,8], finally SkipScanFilter.startKey is [2,8,5,9]. > > >| 448 int currentLength = setStartKey(ptr, minOffset, j+1, nSlots, false); 449 >// From here on, we use startKey as our buffer (resetting minOffset and >maxOffset) 450 // We've copied the part of the current key above that we need >into startKey 451 // Reinitialize the iterator to be positioned at previous >slot position 452 minOffset = 0; 453 maxOffset = startKeyLength; 454 >schema.iterator(startKey, minOffset, maxOffset, ptr, >ScanUtil.getRowKeyPosition(slotSpan, j)+1); 455 // Do nextKey after setting >the accessor b/c otherwise the null byte may have 456 // been incremented >causing us not to find it 457 ByteUtil.nextKey(startKey, currentLength); | > > >From above analysis, we can see the second column is repeatedly copied to >SkipScanFilter.startKey, copy 7 to SkipScanFilter.startKey is error ,before >SkipScanFilter.setStartKey method is invoked in line 448, we should first move >ptr to j+1, that is to say ,following code might be inserted before line 448: > > >schema.reposition( ptr, ScanUtil.getRowKeyPosition(slotSpan, i), >ScanUtil.getRowKeyPosition(slotSpan, j+1), minOffset, maxOffset, >slotSpan[j+1]); > > >Another problem is why the existing SkipScanFilter unit tests are ok? That is >because in all existing unit test cases, backtrack column is just before >current column which ptr points to, i.e. i==j+1, and this problem may not >affect the final query result , but obviously, it may lead to the erroneous >startKey and cause the Skip Scan inefficient.
