I've got a master-slave mysql replication using blackhole engine for some tables on slave, so I'm wondering what will happen if I enable master-master replication? Will the tables become empty on my 1st master?
The answer is: they won't. Replication simply ignoring my blackhole tables. What I have done to test this: Set up docker container with the mysql db. Created a copy of the db to another docker mysql container. Enabled master-master replication on both dbs. Added some different data to both dbs. Changed engine of the couple of tables with BLACKHOLE on the second master. Then I added some different data to both dbs, and checked that on the first master there were no changes in tables that has the BLACKHOLE engine on the second master.