RE: DB Block Buffers - Too Much ???

On Solaris if ISM (intimate shared memory) is enabled and Oracle allocated its shared memory using it (USE_ISM=TRUE) shared memory will not be subject to swapping.

There are equivalent to ISM on other O/S.

Also I think there is one command that could be used to lock the shared segment into memory.

On Solaris: man shmctl --> and search for lock

Hope it helps,

Waleed

-----Original Message-----
From: sean.hull_at_pobox.com [mailto:sean.hull_at_pobox.com] Sent: Wednesday, June 21, 2000 4:58 PM
To: Multiple recipients of list ORACLE-L 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?

Thanks,
Sean

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  INET: sean.hull_at_pobox.com

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