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Date: Mon, 26 Aug 2013 22:26:53 +0000 (UTC)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12662211.1375819562149.35373.1377556013195@arcas>
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Subject: [jira] [Commented] (HDFS-5074) Allow starting up from an fsimage
 checkpoint in the middle of a segment
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    [ https://issues.apache.org/jira/browse/HDFS-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13750654#comment-13750654 ] 

Todd Lipcon commented on HDFS-5074:
-----------------------------------

I may have been incorrect above. HDFS-2709 fixed the above situation for FileJournalManager, but it may not work correctly with QJM. Let's incorporate that fix in this same issue, since I think it's highly related (in pretty much every case we should support opening a segment in the middle)
                
> Allow starting up from an fsimage checkpoint in the middle of a segment
> -----------------------------------------------------------------------
>
>                 Key: HDFS-5074
>                 URL: https://issues.apache.org/jira/browse/HDFS-5074
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: ha, namenode
>    Affects Versions: 3.0.0, 2.1.0-beta
>            Reporter: Todd Lipcon
>
> We've seen the following behavior a couple times:
> - SBN is running and somehow encounters an error in the middle of replaying an edit log in the tailer (eg the JN it's reading from crashes)
> - SBN successfully has processed half of the edits in the segment it was reading.
> - SBN saves a checkpoint, which now falls in the middle of a segment, and then restarts
> Upon restart, the SBN will load this checkpoint which falls in the middle of a segment. {{selectInputStreams}} then fails when the SBN requests a mid-segment txid.
> We should handle this case by downloading the right segment and fast-forwarding to the correct txid.

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