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https://issues.apache.org/jira/browse/CASSANDRA-3862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201610#comment-13201610
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Daniel Doubleday commented on CASSANDRA-3862:
---------------------------------------------
Hmokay ... don't want to abuse Jira as an educational forum but maybe as a
reward for the bugreport :-) ... are you saying that a reader could see a
memtable view where flushing memtables are gone (flushed) and sstables don't
contain the flushed memtables?
If that's the case than yes the cache would lose an update. But that what also
imply that a read could miss an update without caching being in place at all no?
Otherwise (and that's how I read the code) given that the memtable switch will
only happen after the merge the reader will read all updates because they are
either in (flushing) memtables or in sstables and the cache will be in fact
valid.
> RowCache misses Updates
> -----------------------
>
> Key: CASSANDRA-3862
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3862
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.0.7
> Reporter: Daniel Doubleday
> Attachments: include_memtables_in_rowcache_read.patch
>
>
> While performing stress tests to find any race problems for CASSANDRA-2864 I
> guess I (re-)found one for the standard on-heap row cache.
> During my stress test I hava lots of threads running with some of them only
> reading other writing and re-reading the value.
> This seems to happen:
> - Reader tries to read row A for the first time doing a getTopLevelColumns
> - Row A which is not in the cache yet is updated by Writer. The row is not
> eagerly read during write (because we want fast writes) so the writer cannot
> perform a cache update
> - Reader puts the row in the cache which is now missing the update
> I already asked this some time ago on the mailing list but unfortunately
> didn't dig after I got no answer since I assumed that I just missed
> something. In a way I still do but haven't found any locking mechanism that
> makes sure that this should not happen.
> The problem can be reproduced with every run of my stress test. When I
> restart the server the expected column is there. It's just missing from the
> cache.
> To test I have created a patch that merges memtables with the row cache. With
> the patch the problem is gone.
> I can also reproduce in 0.8. Haven't checked 1.1 but I haven't found any
> relevant change their either so I assume the same aplies there.
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