Re: pmap - anon pages

Hi Sybrand ,

Thanks for your message. I am trying to understand the memory allocation and page cache usage of my system . Since i use ocfs , and parallel query , in theory no page cache of redhat linux and oracle buffer cache is in use. But when i monitor the system by using vmstat i see lots of pagings. My first aim is to understand the real reason of these pagings. Do these pagings occur because of file cache (oracle caching ) or not ? (are they just oracle processes anon pages? - With direct io , data that is read from the disk is put directly into the process address space , so the process itself has the data directly , further requests to the same data again needs disk access since no page cache is used.)

My second aim is to size an oracle process. Since this is datawarehouse , and oracle parallel query is mostly used , pga memory is more important than buffer cache. But although i use automatic pga allocation , what i see is most of the oracle processes use 10 or 20 MB. private memory . I have 8gb. of memory , parallel query but only use little amount of private ram but excessive paging (20-30mb. per second - sar -B output) .

You are right that oracle has views to get the pga size for each session and process , (although the values does not exactly match comapring to pmap (no litle differences - great differences ) , but first i want to understand how things happen.

Kind Regards,
hope Received on Thu Jul 28 2005 - 07:28:45 CDT