Will cluster segments work for us

Joe Dunn

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Sep 30, 2016, 5:02:10 PM9/30/16

to codership

Hello,

We are currently running two 3-node clusters with async replication between them. They are not geographically isolated so replication is probably not required. The intent is to use one cluster in production and the second cluster will be used to make database changes for deployments. There are some very large tables that take several days to alter, hence the need for two clusters. When the changes are complete then it will be a very short window to switch over to the modified cluster, then the old cluster can be modified.

The problems arising from using replication in the middle are numerous, but the most troubling is the number of contention messages witnessed on the node acting as the replication master.Then if the master fails it will take a bit of work setting up a new master. As an alternative, it seems that using cluster segments instead of replication would be better. The nodes that are to be modified can be isolated until the changes are made, and switch over would be fast, and easier than switching replication around.

Is is a feasible solution to run what amounts to a 6-node cluster? The transaction rate, from load runner, is about 2900 xact/sec.

Please share your thoughts and experiences,

Thank you.

alexey.y...@galeracluster.com

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Oct 3, 2016, 2:36:49 PM10/3/16

to Joe Dunn, codership

Hi,

No, cluster segments are not working like you think. They don't isolate
the nodes, their purpose is merely to optimize the replication traffic.

What you may want to consider (as it is what you are already practising,
apparently) is rolling schema upgrade with wsrep_OSU_method='RSU'. This
should work provided you don't issue schema-incompatible DMLs during
upgrade.

Kind regards,
Alex

James Wang

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Oct 4, 2016, 5:24:47 AM10/4/16

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What is your MySQL version please? Also, do you use GTID? Is you async Master-Master (or Master-Slave)?

Joe Dunn

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Oct 14, 2016, 8:26:48 PM10/14/16

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MySQL version is 5.6. I have advocated GTID, but currently no. Yes, trying to do it as master-master.

James Wang

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Oct 17, 2016, 4:09:25 AM10/17/16

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I tried M-M Galera clusters - it worked if no GTID (then changing master is an issue).

Have you tried Percona's tool pt-online-schema-change? If there is no triggers on the table(s) you wanna alter, the tool works.

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