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From Anthony John <>
Subject Re: cassandra as session store
Date Tue, 01 Feb 2011 17:57:38 GMT
Not a concern - and here is why:-

>From the wiki arch section captioned below - eventual consistency does not
have to mean inconsistent reads. The concern is the overhead for consistent
reads. But remember in the use case being cited, the expensive read will
happen only during failover, not all the time.

More specifically: R=read replica count W=write replica count N=replication
factor Q=*QUORUM* (Q = N / 2 + 1)


   If W + R > N, you will have consistency
   - W=1, R=N
   - W=N, R=1
   - W=Q, R=Q where Q = N / 2 + 1

On Tue, Feb 1, 2011 at 11:47 AM, Tong Zhu <> wrote:

> The problem is where to store the session data. If the session need to be
> accessible by more than one web servers, the external storage is needed.
> Cassandra only supports eventual consistency. If web server w1 saves the
> session at node 1 of cassendra while web server w2 retrieve the session from
> different node, if these two requests are close enough, there is a chance
> what w2 retrieved is different from what w1 saved. Is it a concern?
> Tong
> -----Original Message-----
> From: buddhasystem []
> Sent: Tuesday, February 01, 2011 9:42 AM
> To:
> Subject: Re: cassandra as session store
> Most if not all modern web application frameworks support sessions. This
> applies to Django (with which I have most experience and also run it with
> X.509 security layer) but also to Ruby on Rails and Pylons.
> So, why would you re-invent the wheel? Too messy. It's all out there for
> you
> to use.
> Regards,
> Maxim
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