"Takayuki Tsunakawa" <tsunakawa.takay@jp.fujitsu.com> writes:
> I wonder whether the field you are talking about set Windows to use
> more memory for programs than for filesystem cache, which is
> selectable from [System] applet of Control Panel (Oh, I wonder how my
> machine is set in this respect... have to check.) If filesystem cache
> is preferred, the following senario may be possible:
> 1. PostgreSQL tries to read data from disk into database cache.
> 2. The kernel tries to allocate filesystem buffers by paging out
> PostgreSQL's memory (possibly shared buffers).
> 3. PostgreSQL finds data requested by its clients in database cache,
> and tries to get it in memory.
> 4. But the shared buffers are paged out, and page-ins happen.
It's certainly true that if shared_buffers is large enough to make the
kernel try to swap out parts of the shared buffer array, then you've got
a counterproductive situation resulting in net *more* I/O than if you'd
used a smaller setting. On some Unixen shared memory is implicitly
locked in RAM, and on others it's possible to request locking it (though
I'm not sure we try to at the moment). Perhaps it's always swappable on
Windows? Or maybe Windows is just more eager to swap it out?
regards, tom lane