Hi!

Question: How do STMM perform on a server with multiple instances?

Is it a good idea or will it be counter productive?

I have seen some white papers on running STMM on a server with multiple databases in one instance but not multiple instances on the same server.

We are running db2 V9.1 fixpak 4a. Som of the servers have up to 10 instances on them.
I would like to turn on STMM on all instances but I'm afraid that it will have strange side effects.

I don't think STMM implementation has to anything with how many instances are running on your server. If your server has sufficient capacity in terms of CPU, Memory, Hardware and it is supporting the existing multiple instances quite well without any Degradation in performance, then the STMM will not do any harm in terms of multiple-instance. STMM makes your life easy if they are properly set as Bufferpool-tuning, Application Group parameters Tuning etc are automatically being taken care of by DB2's Self tuning tool.

If you have multiple instances, then STMM is aware of that and will balance memory across instances, too.