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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2643) Figure how to deal with eof splitting logs
Date Thu, 12 Aug 2010 13:47:16 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897748#action_12897748
] 

stack commented on HBASE-2643:
------------------------------

Good stuff Richard.  If a runtime exception splitting logs, we should fail to start the cluster?
 It means likely dataloss.  Or, there is a flag in hbase now -- its in the splitlog stuff
-- IIRC which says fail-if-any-error OR try-and=keep-going across errors.  If this flag is
set, we should catch the RuntimeException, log it and not start the master.  Otherwise, we
should log the exception and then let the master proceed.

> Figure how to deal with eof splitting logs
> ------------------------------------------
>
>                 Key: HBASE-2643
>                 URL: https://issues.apache.org/jira/browse/HBASE-2643
>             Project: HBase
>          Issue Type: Bug
>            Reporter: stack
>            Priority: Blocker
>             Fix For: 0.90.0
>
>
> When splitting the WAL and encountering EOF, it's not clear what to do. Initial discussion
of this started in http://review.hbase.org/r/74/ - summarizing here for brevity:
> We can get an EOFException while splitting the WAL in the following cases:
> - The writer died after creating the file but before even writing the header (or crashed
halfway through writing the header)
> - The writer died in the middle of flushing some data - sync() guarantees that we can
see _at least_ the last edit, but we may see half of an edit that was being written out when
the RS crashed (especially for large rows)
> - The data was actually corrupted somehow (eg a length field got changed to be too long
and thus points past EOF)
> Ideally we would know when we see EOF whether it was really the last record, and in that
case, simply drop that record (it wasn't synced, so therefore we dont need to split it). Some
open questions:
>   - Currently we ignore empty files. Is it ok to ignore an empty log file if it's not
the last one?
>   - Similarly, do we ignore an EOF mid-record if it's not the last log file?

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