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From Brandon Williams <dri...@gmail.com>
Subject Re: row cache vs frequent row updates vs write through row cache
Date Fri, 05 Nov 2010 20:15:36 GMT
On Fri, Nov 5, 2010 at 2:41 PM, 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.
>

That would be cheaper, yes, but ultimately it's still extra GC if the row is
being mutated often.


> 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?
>

This is a problem too.  You can't make the cache huge because of GC
pressure, and if your read pattern is largely random then the eviction will
cause GC pressure.


> 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.


Row cache is good for a small amount of mostly static rows that are being
read very often (and aren't enormous themselves.)  They don't all have to
fit in the cache, but the working set should to avoid the eviction problem.
 If that's not your use case, don't use row cache.

-Brandon

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