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If I were to set up cyclical replication between a MySQL 5.6 master server and a MySQL 5.1 master server, what are some things that could potentially go wrong?

Also, the 5.6 MySQL does not have GTID enabled.

Thanks IS

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Cringe, gag, etc.

5.1 and 5.6 differ by 2 major versions. Replication is 'guaranteed' to work one direction, not the other.

Don't turn on GTIDs in 5.6; 5.1 will not like it.

Don't use any features new to 5.5 or 5.6.

Simply, don't do it. Get the 5.1 upgraded ASAP.

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  • Agreed. Failure is very likely, in such an environment. To put a fine point on it, this setup isn't guaranteed to work in either direction. "MySQL supports replication from one major version to the next higher major version.". Specifically, that means from and older master and to a newer slave, only. In circular replication, both servers have both roles, and a newer master with an older slave "may be possible, but is generally not supported". There are too many changes for backwards replication to be safe. – Michael - sqlbot Apr 28 '15 at 19:41
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Replication from MySQL 5.x to 5.6 has a bear trap just waiting for you.

In Michael's comment, he stated the politically accept premise : "MySQL supports replication from one major version to the next higher major version.". He also said "this setup isn't guaranteed to work in either direction."

I have a very interesting caveat on going from 5.x to 5.6: There are some rare occasions when a binlog event from a pre-5.6 master cannot be interpreted by 5.6 slave and stops replication cold. I wrote about this in January (See my post mysql replication master 5.5 slave 5.1 error on create database)

I concluded my old post with this

If this crazy scenario was possible from a MySQL 5.5.30 Master to MySQL 5.6.21 Slave, (as I have shown happen and two maintenance cycles to correct), then the reverse is far more likely (the reverse being a new Master and an older Slave).

You do not want circular replication for 5.1/5.6. While you can replicate from 5.1 to 5.6, please don't stay long in that setup. The binlog format differences are very slight, but different enough to break replication. As @RickJames said "Simply, don't do it. Get the 5.1 upgraded ASAP."

While I could expound just on circular replication, I refer you to

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