Re: Monitoring buffercache...

On Mon, 24 Nov 2008, Scott Marlowe wrote:

> My guess is that the period of time for which pg_buffercache takes locks
> on the buffer map are short enough that it isn't a real big deal on a
> fast enough server.

As the server involved gets faster, the amount of time the locks are
typically held for drops.

As your shared_buffers allocation increases, that amount of time goes up.

So how painful the overhead is depends on how fast your CPU is relative to
how much memory is in it.  Since faster systems tend to have more RAM in
them, too, it's hard to say whether the impact will be noticable.

Also, noting that the average case isn't impacted much isn't the concern
here.  The problem is how much having all partition locks held will
increase impact worst-case latency.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD