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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-5074) Allow starting up from an fsimage checkpoint in the middle of a segment
Date Tue, 27 Aug 2013 22:57:52 GMT

     [ https://issues.apache.org/jira/browse/HDFS-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Todd Lipcon updated HDFS-5074:

    Attachment: hdfs-5074.txt

Attached patch should fix the issue.

I removed the {{forReading}} parameter from {{selectInputStreams}} -- it really didn't have
any good use now that we have the ability to fast-forward streams on read to the appropriate
transaction ID. Now, selectInputStreams always returns every log segment which may include
edits >= the requested transaction ID, even if the requested transaction ID falls in the
middle of a segment.

I modified the existing TestFailureToReadEdits to run against both file-based HA and QJM-based
HA. Without the fix, the modified test would fail with similar behavior as described here.

This patch also has a test refactor to create a new test utility class for starting HA clusters
with QJM.
> 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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