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From Jeremy Davis <jerdavis.cassan...@gmail.com>
Subject Re: row cache vs frequent row updates vs write through row cache
Date Fri, 05 Nov 2010 19:41:49 GMT
What do you mean by "Turning Over quickly"? What is Turning over? If it
needs to create an entirely new row, then that would create GC pressure for
sure... But if you are just updating a column in a row that is already in
the cache, then I would think that would be the optimal situation.

OTOH, you may be talking about continuously evicting rows from the cache
(because the cache is too small )... Assuming that is not the case, should I
turn on Row Cache?
In short, it seems like the general advice is unless you have a set of
nearly static rows, AND they all fit in the cache, then rowcache is not
recommended.

-JD

On Fri, Nov 5, 2010 at 11:49 AM, Brandon Williams <driftx@gmail.com> wrote:

> On Fri, Nov 5, 2010 at 1:41 PM, Jeremy Davis <jerdavis.cassandra@gmail.com
> > wrote:
>
>> I saw in the Riptano "Tuning Cassandra" slide deck that the row cache can
>> be detrimental if there are a lot of updates to the cached row. Is this
>> because the cache is not write through, and every update necessitates
>> creation of a new row?
>> I see there is an open issue:
>> https://issues.apache.org/jira/browse/CASSANDRA-860  for implementing
>> write through in 0.8.
>
>
> The problem is that if the row is being updated a lot, the cache is turning
> over quickly, and this exerts GC pressure on the JVM.  Even if it were
> write-through, row cache is probably a bad match for this kind of row, it's
> much better at mostly static rows.  Rely on keycache and OS file cache for
> these instead.
>
> -Brandon
>

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