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https://issues.apache.org/jira/browse/HBASE-15392?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15188566#comment-15188566
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Anoop Sam John commented on HBASE-15392:
----------------------------------------
Index is used to know a row/cell is in which HFile block. Within a block there
may be many rows/cell. To go to particular cell within a block, it is linear
search. Yes you read next Cell see whether this is the one needed if not read
next. There is no indexing within a block. Said that its not generic seek vs
skip.. What Lars say is abt seek within a block. So this seek (within block)
is also some what like read and skip skip way.. But he says the seek is way
slower.. Seeing the code I was not able to judge why it is so slow.. Any idea
u have [~lhofhansl]?
Hope I am answering ur Qs and clearing doubts Daniel.
And yes when the seek point is outside the current block, we wont do skip
skip...
> Single Cell Get reads two HFileBlocks
> -------------------------------------
>
> Key: HBASE-15392
> URL: https://issues.apache.org/jira/browse/HBASE-15392
> Project: HBase
> Issue Type: Sub-task
> Components: BucketCache
> Reporter: stack
> Assignee: stack
> Attachments: 15392-0.98-looksee.txt, 15392.wip.patch,
> 15392v2.wip.patch, 15392v3.wip.patch, 15392v4.patch,
> HBASE-15392_suggest.patch, no_optimize.patch, no_optimize.patch, two_seeks.txt
>
>
> As found by Daniel "SystemTap" Pol, a simple Get results in our reading two
> HFileBlocks, the one that contains the wanted Cell, and the block that
> follows.
> Here is a bit of custom logging that logs a stack trace on each HFileBlock
> read so you can see the call stack responsible:
> {code}
> 2016-03-03 22:20:30,191 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] regionserver.StoreScanner:
> START LOOP
> 2016-03-03 22:20:30,192 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] regionserver.StoreScanner:
> QCODE SEEK_NEXT_COL
> 2016-03-03 22:20:30,192 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileBlockIndex:
> STARTED WHILE
> 2016-03-03 22:20:30,192 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.CombinedBlockCache:
> OUT OF L2
> 2016-03-03 22:20:30,192 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] bucket.BucketCache: Read
> offset=31409152, len=2103
> 2016-03-03 22:20:30,192 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] bucket.FileIOEngine:
> offset=31409152, length=2103
> 2016-03-03 22:20:30,193 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileReaderImpl:
> From Cache [blockType=DATA, fileOffset=2055421, headerSize=33,
> onDiskSizeWithoutHeader=2024, uncompressedSizeWithoutHeader=2020,
> prevBlockOffset=2053364, isUseHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, onDiskDataSizeWithHeader=2053,
> getOnDiskSizeWithHeader=2057, totalChecksumBytes=4, isUnpacked=true,
> buf=[org.apache.hadoop.hbase.nio.SingleByteBuff@e19fbd54],
> dataBeginsWith=\x00\x00\x00)\x00\x00\x01`\x00\x16user995139035672819231,
> fileContext=[usesHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, blocksize=65536, encoding=NONE, includesMvcc=true,
> includesTags=false, compressAlgo=NONE, compressTags=false,
> cryptoContext=[cipher=NONE keyHash=NONE]]]
> 2016-03-03 22:20:30,193 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileReaderImpl:
> Cache hit return [blockType=DATA, fileOffset=2055421, headerSize=33,
> onDiskSizeWithoutHeader=2024, uncompressedSizeWithoutHeader=2020,
> prevBlockOffset=2053364, isUseHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, onDiskDataSizeWithHeader=2053,
> getOnDiskSizeWithHeader=2057, totalChecksumBytes=4, isUnpacked=true,
> buf=[org.apache.hadoop.hbase.nio.SingleByteBuff@e19fbd54],
> dataBeginsWith=\x00\x00\x00)\x00\x00\x01`\x00\x16user995139035672819231,
> fileContext=[usesHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, blocksize=65536, encoding=NONE, includesMvcc=true,
> includesTags=false, compressAlgo=NONE, compressTags=false,
> cryptoContext=[cipher=NONE keyHash=NONE]]]
> java.lang.Throwable
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl.readBlock(HFileReaderImpl.java:1515)
> at
> org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$CellBasedKeyBlockIndexReader.loadDataBlockWithScanInfo(HFileBlockIndex.java:324)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.seekTo(HFileReaderImpl.java:831)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.reseekTo(HFileReaderImpl.java:812)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseekAtOrAfter(StoreFileScanner.java:288)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:198)
> at
> org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:54)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:321)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:279)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:806)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.seekAsDirection(StoreScanner.java:795)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:624)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:153)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:5703)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:5849)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:5622)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:5598)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:5584)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.get(RSRpcServices.java:2187)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.get(RSRpcServices.java:2123)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:33512)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2229)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:109)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:136)
> at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:111)
> at java.lang.Thread.run(Thread.java:745)
> 2016-03-03 22:20:30,193 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileBlockIndex:
> READ [blockType=DATA, fileOffset=2055421, headerSize=33,
> onDiskSizeWithoutHeader=2024, uncompressedSizeWithoutHeader=2020,
> prevBlockOffset=2053364, isUseHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, onDiskDataSizeWithHeader=2053,
> getOnDiskSizeWithHeader=2057, totalChecksumBytes=4, isUnpacked=true,
> buf=[org.apache.hadoop.hbase.nio.SingleByteBuff@e19fbd54],
> dataBeginsWith=\x00\x00\x00)\x00\x00\x01`\x00\x16user995139035672819231,
> fileContext=[usesHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, blocksize=65536, encoding=NONE, includesMvcc=true,
> includesTags=false, compressAlgo=NONE, compressTags=false,
> cryptoContext=[cipher=NONE keyHash=NONE]]]
> 2016-03-03 22:20:30,193 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileBlockIndex:
> DATA BLOCK IS TRUE BREAK
> 2016-03-03 22:20:30,193 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileBlockIndex:
> RETURNING
> 2016-03-03 22:20:30,194 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] regionserver.StoreScanner:
> QCODE INCLUDE
> 2016-03-03 22:20:30,194 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] regionserver.StoreScanner:
> QCODE SKIP
> 2016-03-03 22:20:30,194 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.CombinedBlockCache:
> OUT OF L2
> 2016-03-03 22:20:30,194 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] bucket.BucketCache: Read
> offset=30932992, len=2103
> 2016-03-03 22:20:30,194 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] bucket.FileIOEngine:
> offset=30932992, length=2103
> 2016-03-03 22:20:30,194 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileReaderImpl:
> From Cache [blockType=DATA, fileOffset=2057478, headerSize=33,
> onDiskSizeWithoutHeader=2024, uncompressedSizeWithoutHeader=2020,
> prevBlockOffset=2055421, isUseHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, onDiskDataSizeWithHeader=2053,
> getOnDiskSizeWithHeader=2057, totalChecksumBytes=4, isUnpacked=true,
> buf=[org.apache.hadoop.hbase.nio.SingleByteBuff@6063ac95],
> dataBeginsWith=\x00\x00\x00)\x00\x00\x01`\x00\x16user995698996184959679,
> fileContext=[usesHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, blocksize=65536, encoding=NONE, includesMvcc=true,
> includesTags=false, compressAlgo=NONE, compressTags=false,
> cryptoContext=[cipher=NONE keyHash=NONE]]]
> 2016-03-03 22:20:30,194 TRACE
> [B.defaultRpcServer.handler=20,queue=2,port=16020] hfile.HFileReaderImpl:
> Cache hit return [blockType=DATA, fileOffset=2057478, headerSize=33,
> onDiskSizeWithoutHeader=2024, uncompressedSizeWithoutHeader=2020,
> prevBlockOffset=2055421, isUseHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, onDiskDataSizeWithHeader=2053,
> getOnDiskSizeWithHeader=2057, totalChecksumBytes=4, isUnpacked=true,
> buf=[org.apache.hadoop.hbase.nio.SingleByteBuff@6063ac95],
> dataBeginsWith=\x00\x00\x00)\x00\x00\x01`\x00\x16user995698996184959679,
> fileContext=[usesHBaseChecksum=true, checksumType=CRC32C,
> bytesPerChecksum=16384, blocksize=65536, encoding=NONE, includesMvcc=true,
> includesTags=false, compressAlgo=NONE, compressTags=false,
> cryptoContext=[cipher=NONE keyHash=NONE]]]
> java.lang.Throwable
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl.readBlock(HFileReaderImpl.java:1515)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.readNextDataBlock(HFileReaderImpl.java:906)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.isNextBlock(HFileReaderImpl.java:1106)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.positionForNextBlock(HFileReaderImpl.java:1100)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl._next(HFileReaderImpl.java:1118)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl$HFileScannerImpl.next(HFileReaderImpl.java:1139)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.next(StoreFileScanner.java:152)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:114)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:628)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:153)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:5703)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:5849)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:5622)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:5598)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:5584)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.get(RSRpcServices.java:2187)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.get(RSRpcServices.java:2123)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:33512)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2229)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:109)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:136)
> at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:111)
> at java.lang.Thread.run(Thread.java:745)
> 2016-03-03 22:20:30,195 INFO
> [B.defaultRpcServer.handler=20,queue=2,port=16020] regionserver.StoreScanner:
> QCODE DONE
> {code}
> We are in StoreScanner#next.
> Matcher does SEEK_NEXT_COL.
> We pull in the block that has our Cell in it.
> Matcher does INCLUDE
> Then Matcher does SKIP
> SKIP has us go read the next block.
> Then Matcher does DONE.
> Why ain't I getting to DONE after INCLUDE?
> Any clues?
> This code has been like this a while.
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