I think it all depends on your working set.  Having shared memory be
smaller than you working set causes pages to have to be copied in from
the kernel buffers (not a huge problem, but a small penalty), while
having shared memory larger than the working set causes overhead of
searching through all those buffers.


Vivek Khera wrote:
> >>>>> "TL" == Tom Lane <[EMAIL PROTECTED]> writes:
> TL> Franco Bruno Borghesi <[EMAIL PROTECTED]> writes:
> >> wouldn't also increasing shared_buffers to 64 or 128 MB be a good
> >> performance improvement? This way, pages belonging to heavily used
> >> indexes would be already cached by the database itself.
> TL> Not necessarily.  The trouble with large shared_buffers settings is you
> TL> end up with lots of pages being doubly cached (both in PG's buffers and
> I think if you do a lot of inserting/updating to your table, then more
> SHM is better (and very high fsm settings), since you defer pushing
> out the dirty pages to the disk.  For read-mostly, I agree that
> letting the OS do the caching is a better way.
> -- 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Vivek Khera, Ph.D.                Khera Communications, Inc.
> Internet: [EMAIL PROTECTED]       Rockville, MD       +1-240-453-8497
> AIM: vivekkhera Y!: vivek_khera   http://www.khera.org/~vivek/
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