Sylvain Lebresne created CASSANDRA-6369:
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Summary: Fix prepared statement size computation
Key: CASSANDRA-6369
URL: https://issues.apache.org/jira/browse/CASSANDRA-6369
Project: Cassandra
Issue Type: Bug
Reporter: Sylvain Lebresne
Assignee: Sylvain Lebresne
Fix For: 1.2.12, 2.0.3
When computed the size of CQLStatement to limit the prepared statement cache
(CASSANDRA-6107), we overestimate the actual memory used because the statement
include a reference to the table CFMetaData which measureDeep counts. And as it
happens, that reference is big: on a simple test preparing a very trivial
select statement, I was able to only prepare 87 statements before some started
to be evicted because each statement was more than 93K big and more than 92K of
that was the CFMetaData object. As it happens there is no reason to account the
CFMetaData object at all since it's in memory anyway whether or not there is
prepared statements or not.
Attaching a simple (if not extremely elegant) patch to remove what we don't
care about of the computation. Another solution would be to use the
MemoryMeter.withTrackerProvider option as we do in Memtable, but in the
QueryProcessor case we currently use only one MemoryMeter, not one per CF, so
it didn't felt necessarilly cleaner. We could create one-shot MemoryMeter
object each time we need to measure a CQLStatement but that doesn't feel a lot
simpler/cleaner either. But if someone feels religious about some other
solution, I don't care.
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