Message-Id: <10535.110062@fatcity.com> From: sean.hull@pobox.com Date: Wed, 21 Jun 2000 15:47:53 -0400 (EDT) Subject: Re: DB Block Buffers - Too Much ??? On Wed, 21 Jun 2000, Gaja Krishna Vaidyanatha wrote: > If overallocation is done, and if a significant portion of your > SGA is getting paged/swapped out, then you will experience a > system-wide degradation in performance. Goes to prove that > cache hit ratios by themselves cannot validate that Oracle is > running and functioning optimally. They are just one of the > indicators for performance. You really have to look at the > "amount of work done" or "throughput" on the system and measure > the success of your tuning efforts. Gaja: Your comments on buffer cache hitratios vs OS statistics such as swapping are excellent as usual Gaja. It brings up a question in my mind though. As I recall, one very good system administrator who I used to work with explained to me that certain segments of the SGA seemed to be marked as not-swappable by Oracle. This would certainly leave plenty of room for important components of the Oracle or OS software to be swapped out of memory. The question: Can segments of shared memory be marked by an application as non-swappable, and does Oracle do this? Anybody know, or have pointers to good documents?