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Date: Fri, 22 Jul 2011 15:04:46 -0700
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Subject: Re: question on setup for writes into 2 datacenters
From: Sameer Farooqui <cassandralabs@gmail.com>
To: user@cassandra.apache.org
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It sounds like what you're looking for is write consistency of local_quorum:
http://www.datastax.com/docs/0.8/consistency/index#write-consistency

local_quorum would mean the write has to be successful on a majority of
nodes in DC1 (so 2) before it is considered successful.

If you use just quorum write, it'll have to be committed to 3 replicas out
of the 4 before it's considered successful.


On Fri, Jul 22, 2011 at 1:57 PM, Dean Hiller <dean@alvazan.com> wrote:

> Ideally, we would want to have a replication factor of 4, and a minimum
> write consistency of 2 (which looking at the default in cassandra.yaml is to
> memory first with asynch to disk...perfect so far!!!)
>
> Now, obviously, I can get the partitioner setup to make sure I get 2
> replicas in each data center.  The next thing I would want to guarantee
> however is that if a write came into datacenter 1, it would write to the two
> nodes in datacenter 1 and asynchronously replicate to datacenter 2.  Is this
> possible?  Does cassandra already handle that or is there something I could
> do to get cassandra to do that?
>
> In this mode, I believe I can have both datacenters be live as well as be
> backup for the other not wasting resources.
>
> thanks,
> Dean
>

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It sounds like what you&#39;re looking for is write consistency of local_qu=
orum:<br><a href=3D"http://www.datastax.com/docs/0.8/consistency/index#writ=
e-consistency">http://www.datastax.com/docs/0.8/consistency/index#write-con=
sistency</a><br>
<br>local_quorum would mean the write has to be successful on a majority of=
 nodes in DC1 (so 2) before it is considered successful.<br><br>If you use =
just quorum write, it&#39;ll have to be committed to 3 replicas out of the =
4 before it&#39;s considered successful.<br>
<br><br><br><br><div class=3D"gmail_quote">On Fri, Jul 22, 2011 at 1:57 PM,=
 Dean Hiller <span dir=3D"ltr">&lt;<a href=3D"mailto:dean@alvazan.com">dean=
@alvazan.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" sty=
le=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Ideally, we would want to have a replication factor of 4, and a minimum wri=
te consistency of 2 (which looking at the default in cassandra.yaml is to m=
emory first with asynch to disk...perfect so far!!!)<br><br>Now, obviously,=
 I can get the partitioner setup to make sure I get 2 replicas in each data=
 center.=A0 The next thing I would want to guarantee however is that if a w=
rite came into datacenter 1, it would write to the two nodes in datacenter =
1 and asynchronously replicate to datacenter 2.=A0 Is this possible?=A0 Doe=
s cassandra already handle that or is there something I could do to get cas=
sandra to do that?<br>


<br>In this mode, I believe I can have both datacenters be live as well as =
be backup for the other not wasting resources.<br><br>thanks,<br><font colo=
r=3D"#888888">Dean<br>
</font></blockquote></div><br>

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