Dividing Memory between Oracle 11gR2 and RHEL 6.5

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I have a dedicated server running RHEL 6.5 with 256 GB of RAM and I want it to run Oracle 11g R2. However I don't know how much RAM should I leave for the OS and how much for Oracle. The default installation creates /dev/shm with half the RAM (128GB) but seems a waste to leave the 128 GB for the O/S. I couldn't find any official recommendations from RedHat regarding this.



Configuration and Tuning of Oracle DB on RHEL is collaborative endevour (or should be, anyhow... ;-)

I use the following guide as a baseline for my deployments:

I then work with the DBAs to size out the SGA, etc... to determine how large the Huge Page allocation should be.

I found the video demonstrating the benefits of using tuned and different profiles. (it's RHEL 7) https://access.redhat.com/videos/898563

I don't have a recommendation to answer your question. It really depends (as usual) but as a rule I try to keep Huge Pages under 90% of the entire memory of the host.

Remember that the OS is using that "wasted" space for performance-enhancing activities (like buffering I/Os for disk- and network-based usage). While it's great to say "give ALL the RAM to Oracle," in practice it tends to be a sub-optimal allocation-choice.