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From Dave Gardner <dave.gard...@imagini.net>
Subject Re: row cache vs frequent row updates vs write through row cache
Date Fri, 05 Nov 2010 20:13:21 GMT
> 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.

That's been our experience. Leave the memory for the OS cache instead.

Dave

On Friday, November 5, 2010, Jeremy Davis <jerdavis.cassandra@gmail.com> wrote:
> 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
>
>

-- 
*Dave Gardner*
Technical Architect

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