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From "Kannan Muthukkaruppan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2337) log recovery: splitLog deletes old logs prematurely
Date Thu, 25 Mar 2010 22:52:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12849940#action_12849940
] 

Kannan Muthukkaruppan commented on HBASE-2337:
----------------------------------------------

nice! thanks for the additional testing JD (killing the master while splitting... evil :).

> log recovery: splitLog deletes old logs prematurely
> ---------------------------------------------------
>
>                 Key: HBASE-2337
>                 URL: https://issues.apache.org/jira/browse/HBASE-2337
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: Kannan Muthukkaruppan
>            Assignee: Nicolas Spiegelberg
>            Priority: Blocker
>             Fix For: 0.20.4, 0.21.0
>
>         Attachments: HBASE-2337-20.4.patch
>
>
> splitLog()'s purpose is to take a bunch of commit logs of a crashed RS and create per-region
logs. splitLog() runs in the master.  There are two cases where splitLog() might end up deleting
an old log before actually creating (sync/closing) the newly created logs. If the master crashes
in between deletion of the old log and creation of the new log, then edits could be lost irrecoverably.
> More specifically here are the two issues we (Nicolas, Aravind and I) noticed:
> Issue #1: The old logs are read one at a time. An in memory structure, logEntries (a
map from region name to edits for the region), is populated. And the old logs are closed.
Then the in-memory map is written out to per region files. Fix: We should move the file deletion
to later.
> Issue #2: There is another little case. The per-region log file is written under the
region directory (named oldlogfile.log or the constant HREGION_OLDLOGFILE_NAME). Before the
master creates the file, it checks to see if there is already a file with that name, and if
so, it renames it to oldlogfile.log.old, and then creates file oldlogfile.log again, and copies
over the contents of oldlogfile.log.old to oldlogfile.log. It then proceeds to delete "oldlogfile.log.old",
even though it hasn't closed/sync'ed "oldlogfile.log" yet. 
> --
> I think we should be able to restructure the code such that all deletion of old logs
happens *after* the new logs have been created (i.e. written to & closed).

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