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From "Vijay (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-5357) Query cache
Date Wed, 25 Sep 2013 02:51:07 GMT


Vijay commented on CASSANDRA-5357:

So the cost is quite high vs having live filters
Some synthetic test show very low over head on the filter deserialization

IMHO... Exist check might not be that bad, since 99% (thats a assumption) of the queries will
have the same query filters on them. For those queries which are discreet and present in the
cache (survived the LRU), i think it is fair to take a hit than letting it live in JVM. 
Filters may be big in some cases (like named filters, or filters with long string names) and
even an optimal case of empty strings we still need a minimum of 2 BB, count and the data
structures in memory. Hence a compact storage off-heap might be good.

One other option which we where discussing little earlier, to optimize the filters in the
cache by trying to find the optimal cache filter entry by merging similar and overlapping
queries will help the above.

I'm not concerned about that so much as, do we keep within our total memory budget? 
Ahaa got it, so we need an additional parameter for the cache which says how much memory is
available in the JVM for the cached keys... i will add it to the next revision.
> Query cache
> -----------
>                 Key: CASSANDRA-5357
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>            Assignee: Vijay
> I think that most people expect the row cache to act like a query cache, because that's
a reasonable model.  Caching the entire partition is, in retrospect, not really reasonable,
so it's not surprising that it catches people off guard, especially given the confusion we've
inflicted on ourselves as to what a "row" constitutes.
> I propose replacing it with a true query cache.

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