[HBASE-3006] Reading compressed HFile blocks causes way too many DFS RPC calls severly impacting performance

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.89.20100621
• Fix Version/s: 0.89.20100924, 0.90.0
• Hadoop Flags: Reviewed
• Assignee: Kannan Muthukkaruppan
• Reporter: Kannan Muthukkaruppan
• Created: 16/Sep/10 16:40
• Updated: 20/Nov/15 12:42
• Resolved: 17/Sep/10 03:57

Description

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.

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

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.

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

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