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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3006) Reading compressed HFile blocks causes way too many DFS RPC calls severly impacting performance
Date Thu, 16 Sep 2010 19:59:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12910286#action_12910286
] 

stack commented on HBASE-3006:
------------------------------

Patch looks great to me (This code was robbed from tfile a long time back IIRC).

My sense is that though this a short-lived allocation, allocating compressedSize is overdoing
it and as you suggest, it can vary, possibly widely.  If a cell was large, then we could have
an hfile much larger than 64k.  A buffer of 8 or 16k would just as well save against the 1
byte rpc reads.  If you agree, I can add this in on commit (allocate a 16k buffer by default)?

> 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
>            Assignee: Kannan Muthukkaruppan
>            Priority: Critical
>         Attachments: HBASE-3006.txt
>
>
> 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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