[jira] Commented: (HADOOP-4681) DFSClient block read failures cause open DFSInputStream to become unusable

["stack (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-4681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12712493#action_12712493 ] 

stack commented on HADOOP-4681:
-------------------------------

+1 on patch being applied to TRUNK as well as to 0.20, and 0.19 branches.  DFSClient currently in its treatment of errors is as crude in effect as California's three-strikes rule; any three errors encountered on a file no matter on which of its N blocks and the stream is ruined (See HADOOP-5903 description for more detail though HADOOP-3185 nails the issue way back).

> DFSClient block read failures cause open DFSInputStream to become unusable
> --------------------------------------------------------------------------
>
>                 Key: HADOOP-4681
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4681
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.18.2, 0.19.0, 0.19.1, 0.20.0
>            Reporter: Igor Bolotin
>             Fix For: 0.19.2
>
>         Attachments: 4681.patch
>
>
> We are using some Lucene indexes directly from HDFS and for quite long time we were using Hadoop version 0.15.3.
> When tried to upgrade to Hadoop 0.19 - index searches started to fail with exceptions like:
> 2008-11-13 16:50:20,314 WARN [Listener-4] [] DFSClient : DFS Read: java.io.IOException: Could not obtain block: blk_5604690829708125511_15489 file=/usr/collarity/data/urls-new/part-00000/20081110-163426/_0.tis
> at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.chooseDataNode(DFSClient.java:1708)
> at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.blockSeekTo(DFSClient.java:1536)
> at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.read(DFSClient.java:1663)
> at java.io.DataInputStream.read(DataInputStream.java:132)
> at org.apache.nutch.indexer.FsDirectory$DfsIndexInput.readInternal(FsDirectory.java:174)
> at org.apache.lucene.store.BufferedIndexInput.refill(BufferedIndexInput.java:152)
> at org.apache.lucene.store.BufferedIndexInput.readByte(BufferedIndexInput.java:38)
> at org.apache.lucene.store.IndexInput.readVInt(IndexInput.java:76)
> at org.apache.lucene.index.TermBuffer.read(TermBuffer.java:63)
> at org.apache.lucene.index.SegmentTermEnum.next(SegmentTermEnum.java:131)
> at org.apache.lucene.index.SegmentTermEnum.scanTo(SegmentTermEnum.java:162)
> at org.apache.lucene.index.TermInfosReader.scanEnum(TermInfosReader.java:223)
> at org.apache.lucene.index.TermInfosReader.get(TermInfosReader.java:217)
> at org.apache.lucene.index.SegmentTermDocs.seek(SegmentTermDocs.java:54) 
> ...
> The investigation showed that the root of this issue is that we exceeded # of xcievers in the data nodes and that was fixed by changing configuration settings to 2k.
> However - one thing that bothered me was that even after datanodes recovered from overload and most of client servers had been shut down - we still observed errors in the logs of running servers.
> Further investigation showed that fix for HADOOP-1911 introduced another problem - the DFSInputStream instance might become unusable once number of failures over lifetime of this instance exceeds configured threshold.
> The fix for this specific issue seems to be trivial - just reset failure counter before reading next block (patch will be attached shortly).
> This seems to be also related to HADOOP-3185, but I'm not sure I really understand necessity of keeping track of failed block accesses in the DFS client.

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