You make an interesting distinction that read/write needs more shared
memory.  I think this is because if you want to reused a read-only
shared buffer, you can just throw away the contents, while a dirty
buffer requires you to write it into the kernel before you can use it.


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
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