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https://issues.apache.org/jira/browse/HADOOP-4681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12650802#action_12650802
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Chris Douglas commented on HADOOP-4681:
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The current patch causes about 2x (st x=dfs.client.max.block.acquire.failures)
the number retries for an unrecoverable block. It really retries at N\*x, where
N is the initial value of {{retries}} in DFSClint.DFSInputStream::read. To be
fair, it looks like the current code exercises the same retry logic, but
without resetting {{failures}}, the first exhaustion of sources causes it to
bail out. It's not clear what the semantics are supposed to be in this case,
but it's worth noting that this patch would change them.
bq. 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.
IIRC, the intent of HADOOP-3185 was to avoid filling the deadNodes list with
good nodes hosting earler, bad blocks. It also improves on the quick fix in
HADOOP-1911.
I haven't been able to find a path where applying the patch reintroduces an
infinite loop.
> 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
> Affects Versions: 0.18.2, 0.19.0, 0.19.1, 0.20.0
> Reporter: Igor Bolotin
> Fix For: 0.19.1, 0.20.0
>
> 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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