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https://issues.apache.org/jira/browse/CASSANDRA-3862?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-3862:
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Attachment: 3862-7.txt
v7 attached.
bq. Since we don't add stuffs to the sentinel, it has no reason to be a
subclass of ColumnFamily
True, but when I tried this I ended up with a LOT of casting cache values to
CF. I think it might be the lesser of evils the way it is.
bq. the counter special case is not needed anymore
Updated.
bq. if we fail to replace the sentinel, I think we should still better return
the data rather than looping and re-reading
Makes sense, updated.
bq. Is it really an improvement to use UUIDs (over an AtomicLong)?
I'd rather have the reduced contention on instantiation than the 8 bytes of
space (during the sentinel lifetime -- this goes away once the sentinel is
replaced by the data CF).
> RowCache misses Updates
> -----------------------
>
> Key: CASSANDRA-3862
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3862
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 0.6
> Reporter: Daniel Doubleday
> Assignee: Sylvain Lebresne
> Fix For: 1.1.0
>
> Attachments: 3862-7.txt, 3862-cleanup.txt, 3862-v2.patch,
> 3862-v4.patch, 3862-v5.txt, 3862-v6.txt, 3862.patch, 3862_v3.patch,
> 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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