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From "Kannan Muthukkaruppan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2337) log recovery: splitLog deletes old logs prematurely
Date Wed, 17 Mar 2010 17:25:27 GMT
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


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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