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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4128) 2NN gets stuck in inconsistent state if edit log replay fails in the middle
Date Mon, 29 Oct 2012 21:26:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486382#comment-13486382
] 

Todd Lipcon commented on HDFS-4128:
-----------------------------------

The issue is that it's starting replay at the beginning of the next full segment, instead
of starting with the previous half-replayed segment and skipping forward to the correct txid.
We could either fix this, or change the 2NN so that if edit log replay fails, it aborts itself
entirely (given such errors are generally going to just happen again on the next attempt,
it's probably better to fail hard so an admin notices, instead of retrying forever)
                
> 2NN gets stuck in inconsistent state if edit log replay fails in the middle
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-4128
>                 URL: https://issues.apache.org/jira/browse/HDFS-4128
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 2.0.2-alpha
>            Reporter: Todd Lipcon
>
> We saw the following issue in a cluster:
> - The 2NN downloads an edit log segment:
> {code}
> 2012-10-29 12:30:57,433 INFO org.apache.hadoop.hdfs.server.namenode.FSImage: Reading
/xxxxxxx/current/edits_0000000000049136809-0000000000049176162 expecting start txid #49136809
> {code}
> - It fails in the middle of replay due to an OOME:
> {code}
> 2012-10-29 12:31:21,021 ERROR org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader:
Encountered exception on operation AddOp [length=0, path=/xxxxxxxx
> java.lang.OutOfMemoryError: Java heap space
> {code}
> - Future checkpoints then fail because the prior edit log replay only got halfway through
the stream:
> {code}
> 2012-10-29 12:32:21,214 INFO org.apache.hadoop.hdfs.server.namenode.FSImage: Reading
/xxxxx/current/edits_0000000000049176163-0000000000049177224 expecting start txid #49144432
> 2012-10-29 12:32:21,216 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode:
Exception in doCheckpoint
> java.io.IOException: There appears to be a gap in the edit log.  We expected txid 49144432,
but got txid 49176163.
> {code}

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