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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1263) 0.20: in tryUpdateBlock, the meta file is renamed away before genstamp validation is done
Date Wed, 23 Jun 2010 17:35:50 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881776#action_12881776
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Todd Lipcon commented on HDFS-1263:
-----------------------------------

bq. also, we check the genstamp is moving upwards both at the start of updateBlock and at
the end of tryUpdateBlock. do you know why?

Oops, missed this question - probably because synchronization blocks are dropped and reclaimed
in every cycle of checking that no threads are writing the block. But we should certainly
do the sanity check at the top of the function instead of after renaming the meta file

> 0.20: in tryUpdateBlock, the meta file is renamed away before genstamp validation is
done
> -----------------------------------------------------------------------------------------
>
>                 Key: HDFS-1263
>                 URL: https://issues.apache.org/jira/browse/HDFS-1263
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.20-append
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.20-append
>
>
> Saw an issue where multiple datanodes are trying to recover at the same time, and all
of them failed. I think the issue is in FSDataset.tryUpdateBlock, we do the rename of blk_B_OldGS
to blk_B_OldGS_tmpNewGS and *then* check that the generation stamp is moving upwards. Because
of this, invalid update block calls are blocked, but they then cause future updateBlock calls
to fail with "Meta file not found" errors.

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