I have a master I was going to start slaving to a new server to do some tests on. This master is currently being slaved to 3 other boxes.
After bringing the new slave online it became clear it wasn't able to keep up. I was hoping this was just an issue of caches needing to get warmed, but after a couple hours it was clear it was just falling farther and farther behind.
It's not as beefy hardware wise as the other slaves (less ram, slower disks) so that seemed like likely culprites.
However one thing that seemed odd was right around the time the new slave started going the other preexisting slave, which had no problem keeping up with the load for that time of day started falling farther and farther behind as well.
Any pointers on what to look at or why this might have happened. We're running MySQL 5.1. The new slave is in the same DC as the master and preexisting slave.
Edit: After we stopped slaving on the new slave to get some faster disks in, the preexistings slave's replication started to catch up again.
Edit: (Solution Found) I had copied a my.cnf from another slave (the one that was falling behind mysteriously). I updated some configs such as innodb buffer size to be more appropriate for the memory the new slave had but neglected to update the server-id. Apparently mysql does nothing to prevent this but everything described in http://bugs.mysql.com/bug.php?id=16927 was going on (Slave error's mentioned in the error log, an INSANE amount of relay logs getting generated).
I updated the server id on the new slave and things look to be going well. Well, insofar as it's not causing the other slaves to fall behind.