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From "Branimir Lambov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9669) If sstable flushes complete out of order, on restart we can fail to replay necessary commit log records
Date Wed, 19 Aug 2015 09:54:46 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14702785#comment-14702785
] 

Branimir Lambov commented on CASSANDRA-9669:
--------------------------------------------

Should we really ignore the timespan before the first known sstable interval? This can break
correct replay for a fresh table, can't it (if the first two flushes are initiated close together
and the node dies after the latter completes early)?

{{CompactionManager.instance.submitBackground(cfstore)}} in [permitCompactionOfFlush|https://github.com/apache/cassandra/compare/trunk...belliottsmith:9669-2.0#diff-06edf300ef64021a42929f19d0cfba3bR185]
is new and appears to be a change in behaviour. Could you explain in a comment why it is now
necessary?

[SSTableMetadata.deserialize|https://github.com/apache/cassandra/compare/trunk...belliottsmith:9669-2.0#diff-0c40f7e67fc53dd15d5fe193e55b2b04R494]:
is there a reason to pass {{hasCommitLogLowerBound}} around separately when it always matches
the one in the passed descriptor?

> If sstable flushes complete out of order, on restart we can fail to replay necessary
commit log records
> -------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-9669
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9669
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>            Priority: Critical
>              Labels: correctness
>             Fix For: 3.x, 2.1.x, 2.2.x, 3.0.x
>
>
> While {{postFlushExecutor}} ensures it never expires CL entries out-of-order, on restart
we simply take the maximum replay position of any sstable on disk, and ignore anything prior.

> It is quite possible for there to be two flushes triggered for a given table, and for
the second to finish first by virtue of containing a much smaller quantity of live data (or
perhaps the disk is just under less pressure). If we crash before the first sstable has been
written, then on restart the data it would have represented will disappear, since we will
not replay the CL records.
> This looks to be a bug present since time immemorial, and also seems pretty serious.



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