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? Received on Wed Jun 21 2000 - 14:47:53 CDT