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From: Brandon Williams <driftx@gmail.com>
Date: Fri, 5 Nov 2010 13:49:38 -0500
Message-ID: <AANLkTinjLN-kSanghoxDrhGNpDr=X1QeqDY2SbWmabnW@mail.gmail.com>
Subject: Re: row cache vs frequent row updates vs write through row cache
To: user@cassandra.apache.org
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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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<div class=3D"gmail_quote">On Fri, Nov 5, 2010 at 1:41 PM, Jeremy Davis <sp=
an dir=3D"ltr">&lt;<a href=3D"mailto:jerdavis.cassandra@gmail.com">jerdavis=
.cassandra@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex=
;">

I saw in the Riptano &quot;Tuning Cassandra&quot; slide deck that the row c=
ache 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? <br>


I see there is an open issue: <a href=3D"https://issues.apache.org/jira/bro=
wse/CASSANDRA-860" target=3D"_blank">https://issues.apache.org/jira/browse/=
CASSANDRA-860</a>=A0 for implementing write through in 0.8.</blockquote><di=
v>

<br></div><div>The problem is that if the row is being updated a lot, the c=
ache is turning over quickly, and this exerts GC pressure on the JVM. =A0Ev=
en if it were write-through, row cache is probably a bad match for this kin=
d of row, it&#39;s much better at mostly static rows. =A0Rely on keycache a=
nd OS file cache for these instead.</div>

<div><br></div><div>-Brandon=A0</div></div>

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