Use of pt-table-checksum in master-master environments

This topic follows this question on Launchpad

The original question was:
I would like to know if it is safe (from the replication point of view) to run pt-table-checksum toolkit in environments with a master-master MySQL configuration with slaves like this one:

A == B| |C D

[] A is slave of B B is slave of A
] C is slave of A D is slave of B
The documentation of the pt-table-checksum do not discuss about such a configuration, unlike the pt-table-sync documentation for example.

In addition to the safety of the tool, I would like also to know if running pt-table-checksum on server A, automatically make the checksums on all the other servers.

The last question was:

I agree with your reply (that of Baron), just wondering why are you referring to a “passive master”.

The configuration I have explained is an active-active master-master replication where both A and B are active masters. The same arguments can be applied also in this case?

Thank you for your attention.

One of the cardinal rules of MySQL replication is that you should never write to more than one server. Based on that, you should have an active/passive master/master configuration, and you should run this tool on the active master, not the passive master, because the writes should all go to one server.

Obviously I agree with the rule, in this case both servers are active for different projects/schema in order to distribute the load and avoid to have a single server heavy loaded and the other one in standby.
So applying your suggestion to our structure leads to run the pt-table-checksum on one schema at a time on the active master for that schema/project.

Thanks for you clarification.