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XCDR with more than two data centers

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Mon, 01/28/2013 - 14:34
ac1dr41n
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I'm trying to figure out if Couchbase 2.0 will support XDCR with more than two data centers? All the documentation I read on the site specifically talk about two datacenters, but what if we want to set up omni-directional replication across more than two? I'm thinking something similar to whats shown in the pretty Earth graph on the bottom of this page:

http://blog.couchbase.com/stabilizing-couchbase-server-2-dot-0

Based on that, it seems "do-able", but I don't see anything in the documentation that specifically says it will work, or how to set it up.

Can somebody clarify? Can we set up 3 or 4 data centers and control what replicates to where? Ultimately it really comes down to whether or not a single cluster can have two "master" clusters to receive replication from into a single bucket. For example, can "vBucket 1" on cluster 2 receive incoming replication from both vBucket 1 on Cluster 1 and vBucket 1 on cluster 3?

Thanks in advance for help.....

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Wed, 01/30/2013 - 10:43
tgrall
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Hello,

Yes you can use XDCR with more than 2 data centers.

Have you looked at the documentation:
- http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-admin-tasks...
- http://www.couchbase.com/presentations (great webinar about it)

Note that XDCR deals with "Bucket" (not vBuckets)

Regards

__________________

Tug
@tgrall

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Wed, 01/30/2013 - 11:14
ac1dr41n
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Thanks for the feedback. Yes, I did read through the documentation, but I didn't see much specifics about setting up more than two datacenters.

To be clear, I don't mean that I want a node in each of three data centers. In fact, I want a three node cluster in DC1, a separate three node cluster in DC2, and another separate three node cluster in DC3. Then, I want to set up master-master replication between a node in DC1 and DC2. And then a separate master-master between another node in DC1 and DC3. And just to be complete, master-master between another node in DC2 one in DC3.

I did see on the FAQ, that to set up master-master you simply pick a node in the cluster on each side, and use that for your standar MySQL master-master replication. I guess the question is, if I do that, can I then set up an additional master-master off another node in to go to a completely different cluster?

By the way, in the list of presentations, which one specifically discusses this? I searched the page for XDCR, and didnt see anything.

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Wed, 01/30/2013 - 11:31
tgrall
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Sorry for the link, the Webinar is located here:
http://info.couchbase.com/BetaWebinar4WebinarRegistrationPage.html

a new one on XDCR will happen on Fev 27th - http://www.couchbase.com/webinars

I will find more informations for you too / bring the expert

Regards

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Tug
@tgrall

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Wed, 01/30/2013 - 11:35
ac1dr41n
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Awesome! Thanks! Any info you can provide would be most appreciated!

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Wed, 01/30/2013 - 11:38
ac1dr41n
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Sorry, I meant to say "MySQL-like" replication....

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Wed, 01/30/2013 - 12:49
dipti
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Yes, you can replicate to two or more data centers.

Let's say you have DC1 (5 node cluster) DC2 ( 6 node cluster) DC3 (7 node cluster)

You setup replication as several unidirectional replications as follows:

DC1 -> DC2
DC2 -> DC1
DC2 -> DC3
DC3 -> DC1
DC1 -> DC3
DC3 -> DC1

this is a ring configuration. You will have to size the clusters to ensure they can not only handle incoming workload but also replication workload (CPU , IO, memory impact)

Read about some of the different topologies in our white paper: http://info.couchbase.com/rs/northscale/images/Couchbase_WP_Cross_Datace...

In addition, the webinar will help you understand how it works.

For sizing: we have a blog coming out that explains more details of XDCR on the system. I'll update this post once, we post it.

hope this helps.

- Dipti

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Wed, 01/30/2013 - 12:53
dipti
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Oh and btw, this is for master - master setup. If you just want a hot standby, you can simply have unidirectional replication.

Also, look at the tunables here: These could have a big impact on performance based on what your application requirements are. Its a balance between more network communication and lower latency. XDCR is linearly scalable so as your write workload increases, to increase XDCR throughput, adding more nodes will help.

Viewing settings
http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-admin-resta...

Changing settings:
http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-admin-resta...

Example:
http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-admin-xdcr-...

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Wed, 01/30/2013 - 13:03
ac1dr41n
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Thanks a ton!

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