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Sylvain Lebresne commented on CASSANDRA-2105:
---------------------------------------------
I plan to reuse the fix I had made for #1546 that uses a ReadWriteLock to fix
this (unless I find a better idea in the meantime). Unless proven otherwise I
don't think this will have a huge impact on counter read performance, but if
someone finds a better idea, I'm listening.
> Fix the read race condition in CFStore for counters
> ----------------------------------------------------
>
> Key: CASSANDRA-2105
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2105
> Project: Cassandra
> Issue Type: Bug
> Affects Versions: 0.8
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Labels: counters
> Fix For: 0.8
>
>
> There is a (known) race condition during counter read. Indeed, for standard
> column family there is a small time during which a memtable is both active and
> pending flush and similarly a small time during which a 'memtable' is both
> pending flush and an active sstable. For counters that would imply sometime
> reconciling twice during a read the same counterColumn and thus over-counting.
> Current code changes this slightly by trading the possibility to count twice a
> given counterColumn by the possibility to miss a counterColumn. Thus it trades
> over-counts for under-counts.
> But this is no fix and there is no hope to offer clients any kind of guarantee
> on reads unless we fix this.
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