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From "Kannan Muthukkaruppan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-3006) Reading compressed HFile blocks causes way too many DFS RPC calls severly impacting performance
Date Thu, 16 Sep 2010 16:41:32 GMT
Reading compressed HFile blocks causes way too many DFS RPC calls severly impacting performance
-----------------------------------------------------------------------------------------------

                 Key: HBASE-3006
                 URL: https://issues.apache.org/jira/browse/HBASE-3006
             Project: HBase
          Issue Type: Bug
    Affects Versions: 0.89.20100621
            Reporter: Kannan Muthukkaruppan
            Priority: Critical


On some read perf tests, we noticed several perf outliers (10 second plus range). The rows
were large (spanning multiple blocks, but still the numbers didn't add up). We had compression
turned on.

We enabled DN clienttrace logging,
log4j.logger.org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace=DEBUG

and noticed lots of 516 byte reads at the DN level, several of them at the same offset in
the block.

{code}
2010-09-16 09:28:32,335 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:38713, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 203000
2010-09-16 09:28:32,336 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:40547, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 119000
2010-09-16 09:28:32,337 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:40650, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 149000
2010-09-16 09:28:32,337 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:40861, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 135000
2010-09-16 09:28:32,338 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:41129, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 117000
2010-09-16 09:28:32,339 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:41691, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 148000
2010-09-16 09:28:32,339 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:42881, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 114000
2010-09-16 09:28:32,341 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:49511, bytes: 516, op: HDFS_READ, cliID: DFSClient_-436329957,
offset: 39884800, srvID: DS-1757894045-10.3\
0.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 153000
2010-09-16 09:28:32,342 INFO org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace:
src: /10.30.251.189:50010, dest: /10.30.251.189:51158, bytes: 3096, op: HDFS_READ, cliID:
DFSClient_-436329957, offset: 39884800, srvID: DS-1757894045-10.\
30.251.189-50010-1283993662994, blockid: blk_-4686540439725119008_1985, duration: 139000
{code}

This was strange coz our block size was 64k, and on disk block size after compression should
generally have been around 6k.

Some print debugging at the HFile and BoundedRangeFileInputStream (which is wrapped by createDecompressionStream)
revealed the following:

We are trying to read 20k from DFS @ HFile layer. The BounderRangeFileInputStream instead
reads several header bytes 1 byte at a time, and then reads a 11k chunk and later a 9k chunk.

{code}
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.HFile: ### fs read @ offset
= 34386760 compressedSize = 20711 decompressedSize = 92324
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386760; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386761; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386762; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386763; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386764; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386765; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386766; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386767; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34386768; bytes: 11005
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397773; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397774; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397775; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397776; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397777; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397778; bytes: 1
2010-09-16 09:21:27,912 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397779; bytes: 1
2010-09-16 09:21:27,913 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397780; bytes: 1
2010-09-16 09:21:27,913 INFO org.apache.hadoop.hbase.io.hfile.BoundedRangeFileInputStream:
### seeking to reading @ 34397781; bytes: 9690
{code}

Seems like it should be an easy fix to prefetch the compressed size... rather than incremental
fetches.


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