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Date: Tue, 14 Jul 2009 14:33:52 +0100
Message-ID: <ff1a07b80907140633n78c09d25o619f717dce3e41f1@mail.gmail.com>
Subject: Re: Scaling from 1 to x (was: one server or more servers?)
From: Mark Robson <markxr@gmail.com>
To: cassandra-user@incubator.apache.org
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2009/7/14 Johan Stuyts <j.stuyts@zybber.nl>

> One of the purposes I want to use Cassandra for is custom HTTP session
> replication. Instead of storing the values in the session of the servlet
> container I want to store them individually using unique keys in Cassandra.
> I was hoping Cassandra would be fast enough for this.


Fast enough - yes. Consistent enough - probably not.

As it's a http session application, you really, really want writes to be
visible from anywhere immediately. If you're using it for authentication
(for example "keep me logged in for today" type function), then you'll need
to get the absolute latest value from the session.

The user will log on and expect to be logged on immediately, and be able to
switch to different web servers transparently without being asked to log on
again.

Cassandra doesn't provide the guarantees about the latest changes being
available from any given node, so you can't really use it in such an
application.

I don't know if the "blocking" variants of the write operations make any
more guarantees, if they do then it might be suitable.

Mark

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<br><br><div class=3D"gmail_quote">2009/7/14 Johan Stuyts <span dir=3D"ltr"=
>&lt;<a href=3D"mailto:j.stuyts@zybber.nl">j.stuyts@zybber.nl</a>&gt;</span=
><br><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(=
204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

One of the purposes I want to use Cassandra for is custom HTTP session repl=
ication. Instead of storing the values in the session of the servlet contai=
ner I want to store them individually using unique keys in Cassandra. I was=
 hoping Cassandra would be fast enough for this.</blockquote>
<div><br></div></div>Fast enough - yes. Consistent enough - probably not.<b=
r><br>As it&#39;s a http session application, you really, really want write=
s to be visible from anywhere immediately. If you&#39;re using it for authe=
ntication (for example &quot;keep me logged in for today&quot; type functio=
n), then you&#39;ll need to get the absolute latest value from the session.=
<br>
<br>The user will log on and expect to be logged on immediately, and be abl=
e to switch to different web servers transparently without being asked to l=
og on again.<br><br>Cassandra doesn&#39;t provide the guarantees about the =
latest changes being available from any given node, so you can&#39;t really=
 use it in such an application.<br>
<br>I don&#39;t know if the &quot;blocking&quot; variants of the write oper=
ations make any more guarantees, if they do then it might be suitable.<br><=
br>Mark<br>

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