Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@cassandra.apache.org
Received-SPF: pass (athena.apache.org: domain of dave.gardner@imagini.net
 designates 209.85.215.44 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <AANLkTimXWWOjAApTczDnOV5HfBVFRY=m0VFGbHiHeir-@mail.gmail.com>
References: <AANLkTi=qsgrru+CdTKJ2O-Co3Tua8Rc3vvnLv+SzpopK@mail.gmail.com>
	<AANLkTinjLN-kSanghoxDrhGNpDr=X1QeqDY2SbWmabnW@mail.gmail.com>
	<AANLkTimXWWOjAApTczDnOV5HfBVFRY=m0VFGbHiHeir-@mail.gmail.com>
Date: Fri, 5 Nov 2010 20:13:21 +0000
Message-ID: <AANLkTin0hR1q-kR6y76Tn0jt9zyPZD_zwpaMu+2J-2qz@mail.gmail.com>
Subject: Re: row cache vs frequent row updates vs write through row cache
From: Dave Gardner <dave.gardner@imagini.net>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

> In short, it seems like the general advice is unless you have a set of ne=
arly static rows, AND they all fit in the cache, then rowcache is not recom=
mended.

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> wr=
ote:
> What do you mean by "Turning Over quickly"? What is Turning over? If it n=
eeds 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 t=
he 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 ne=
arly static rows, AND they all fit in the cache, then rowcache is not recom=
mended.
>
> -JD
>
> On Fri, Nov 5, 2010 at 11:49 AM, Brandon Williams <driftx@gmail.com> wrot=
e:
>
> On Fri, Nov 5, 2010 at 1:41 PM, Jeremy Davis <jerdavis.cassandra@gmail.co=
m> 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 be=
cause the cache is not write through, and every update necessitates creatio=
n of a new row?
> I see there is an open issue: https://issues.apache.org/jira/browse/CASSA=
NDRA-860=A0 for implementing write through in 0.8.
>
>
>
> The problem is that if the row is being updated a lot, the cache is turni=
ng over quickly, and this exerts GC pressure on the JVM. =A0Even 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. =A0Rely on keycache and OS file cache =
for these instead.
>
>
>
> -Brandon
>
>

--=20
*Dave Gardner*
Technical Architect

[image: imagini_58mmX15mm.png]   [image: VisualDNA-Logo-small.png]

*Imagini Europe Limited*
7 Moor Street, London W1D 5NB

[image: phone_icon.png] +44 20 7734 7033
[image: skype_icon.png] daveg79
[image: emailIcon.png] dave.gardner@imagini.net
[image: icon-web.png] http://www.visualdna.com

Imagini Europe Limited, Company number 5565112 (England
and Wales), Registered address: c/o Bird & Bird,
90 Fetter Lane, London, EC4A 1EQ, United Kingdom