RE: Question about SGA memory allocation and sizing

Apologies in advance if what I'm about to mention isn't news to you!

With a massive SGA, no huge pages, and lots of concurrently active sessions, the amount of memory used for the page table might be enough to topple the server via a swap storm. For instance, I have seen a system with a 40 or so GB buffer cache and 22GB of memory being used for page tables. There is a great presentation that shows you how to calculate page table memory usage based on the number of processes and the size of your SGA: http://www.pythian.com/news/741/pythian-goodies-free-memory-swap-oracle-and-everything . grep PageT /proc/meminfo will show you how much memory is used for the page table. I'd probably be tempted to crank your memory target right down and avoid the possibility of "a perfect storm" (where oracle is using all the allowed memory and lots of processes are active) until you get can get HugePages implemented.

Hope that helps

Austin

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