I have a UNIX server running AIX. It has 4 cpus with a total of 16 GB of memory. How do I determine how much memory needs to be left to run the operating system? What is left over will be split between the SGAs and PGAs of four Oracle instances.
I have read Oracle's concepts, tuning, and reference manuals on the subject of allocating memory to the SGA and PGA. I do not want to know how to set those parameters. I just want to know how much of my 16 GB to leave to meet the needs of the operating system.
If you can point me to a reference, I would appreciate that. If you can tell me of your personal experience with this, I would appreciate that too.
Read this doc
How SGA_MAX_SIZE Parameter Works [ID 260171.1]
OS RAM — 20 percent of total RAM for MS-Windows, 10% of RAM for UNIX
Oracle SGA RAM — determined with the show sga command
As far as I'm aware there is no better way to determine how much RAM your OS needs beside checking the setup or installation documentation for your version of AIX and add the memory requirements of your installed peripherals.