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https://issues.apache.org/jira/browse/HDFS-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13736144#comment-13736144
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Todd Lipcon commented on HDFS-5074:
-----------------------------------
Yes, the Tailer will retry and will read from a different JN the next time
around. When it does so, it properly "fast-forwards" the stream to the right
transaction. But, if a checkpoint was overdue, it may make a checkpoint before
it gets a chance to retry, which can provoke this issue on the next restart of
the SBN if it doesn't make an "aligned" checkpoint before then.
> 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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