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From "Giri (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5074) Allow starting up from an fsimage checkpoint in the middle of a segment
Date Thu, 03 Oct 2013 07:23:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13784884#comment-13784884
] 

Giri commented on HDFS-5074:
----------------------------

The namenode log is:

2013-09-26 10:44:41,914 FATAL org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer: Unknown
error encountered while tailing edits. Shutting down standby NN.
java.io.IOException: There appears to be a gap in the edit log.  We expected txid 26, but
got txid 5400.
	at org.apache.hadoop.hdfs.server.namenode.MetaRecoveryContext.editLogLoaderPrompt(MetaRecoveryContext.java:94)
	at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadEditRecords(FSEditLogLoader.java:183)
	at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadFSEdits(FSEditLogLoader.java:111)
	at org.apache.hadoop.hdfs.server.namenode.FSImage.loadEdits(FSImage.java:733)
	at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer.doTailEdits(EditLogTailer.java:227)
	at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.doWork(EditLogTailer.java:321)
	at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.access$200(EditLogTailer.java:279)
	at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread$1.run(EditLogTailer.java:296)
	at org.apache.hadoop.security.SecurityUtil.doAsLoginUserOrFatal(SecurityUtil.java:456)
	at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.run(EditLogTailer.java:292)
2013-09-26 10:44:41,917 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 1

> 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
>            Assignee: Todd Lipcon
>         Attachments: hdfs-5074.txt
>
>
> 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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