Benedict created CASSANDRA-6919:
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Summary: Use OpOrder to guard sstable references for reads,
instead of acquiring/releasing references
Key: CASSANDRA-6919
URL: https://issues.apache.org/jira/browse/CASSANDRA-6919
Project: Cassandra
Issue Type: Improvement
Reporter: Benedict
Assignee: Benedict
Priority: Minor
Fix For: 2.1 beta2
To slightly improve CASSANDRA-6916, and because it's a bit of a simplification
anyway, we should move to ensuring sstable resources remain around during reads
by guarding them with an OpOrder (which is also being introduced for
CASSANDRA-6694) instead of using markReferenced()/release.
Note this does not eliminate markReferenced, as for long running processes such
as compaction it makes sense to have an independent mechanism, because these
long running processes would prevent all resource cleanup for their duration
rather than just the resources they're using.
All this does is cleanup and slightly optimise the read path, whilst giving
better guarantees about resource cleanup (e.g. page cache dropping of old
sstables which may have been replaced multiple times since the reader was
created, so we are dropping pages we don't realise are still in use - in real
terms it should be very rare for such a reader to outlive multiple replacements
and this is only a performance issue, not a matter of correctness, but it's
nice to absolutely be certain anyway).
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