We have a database server running Centos 5.6 64bit 64Gb of RAM. The server is idle most of the time. However, every hour it gets a lot of DELAYED inserts. Up to 3 mil INSERTs per hour into a MyISAM table. The version of MySQL is: 5.1.56-community-log
For some reason, the server eventually eats all the memory it has, goes into swap and becomes very slow. Even after NOTHING else is happening on the server, it stays that way.
Here's a picture showing htop:
How we do these inserts. There's a job every hour that runs on a server and starts doing a lot of inserts. All inserts are DELAYED. Inserts are NOT extended but we use mysqli::multiple_query to send 2500 of these single statement inserts to the server in one batch.
What would also help is to look inside MySQL and see where it's consuming all that memory. We've already checked all the usual buffers and they are way below the amount of memory we have.