Env: DB2 9.5 on AIX.
I am trying to correlate system memory with DB2’s BP and various Heap sizes. The system has only DB2 (it is dedicated database server). My AIX admin says that almost all available memory is being used by DB2 (system memory is 64 GB & DB2 uses 75% of it per AIX admin). But, when I add all the Heap sizes and Bufferpools, I get a small number (in the range of 12 GB) which throws me off. Tracking memory using db2mtrk also shows less amount of memory being used.

Will DB2 use extra memory if it sees as available? Then, what is the point in setting BP and heaps?

UNIX and Linux operating systems will allocate any memory not used by applications for file caching, and give the memory back to the applications if needed. For some reason, many UNIX/Linux system admins don't really understand how the OS works.

Ask your admin to calculate how much of that memory he says is in use, is actually being used by file system caching instead of applications like DB2.

However, one thing you can do to reduce file system caching is to disable file system caching for all DMS tablespaces as recommended by IBM for better performance (alter tablespace command). For tablespaces with LOB data (hopefully your LOB data is in a separate LONG tablespace), you should enable file system caching. For various technical reasons, you should also have file system caching on for SMS tablespaces.

If the server is dedicated for DB2, The computation memory of the server ( this is show in the memory output of topas command ) is approximately equal to memory used by db2。
After 9.5 or later， You can use db2pd -dbptn to see how db2 used system memory....

Thanks for the reply, Marcus_A & fengsun2. That's helpful.