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Date: Wed, 23 Jun 2010 13:35:50 -0400 (EDT)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1263) 0.20: in tryUpdateBlock, the meta
 file is renamed away before genstamp validation is done
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    [ https://issues.apache.org/jira/browse/HDFS-1263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881776#action_12881776 ] 

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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