Re: pg_buffercache's usage count

Alvaro Herrera wrote:
> BTW the only reason you don't see buffers having a larger "usage" is
> that the counters are capped at that value.
>

Right, the usage count is limited to 5 for no reason besides "that seems
like a good number".  We keep hoping to come across a data set and
application with a repeatable benchmark where most of the data ends up
at 5, but there's still a lot of buffer cache churn, to allow testing
whether a further increase could be valuable.  So far nobody has
actually found such a set.  If I shrunk shared_buffers on Ben's data I
think I could create that situation.  As is usually the case, I doubt he
has another server with 128GB of RAM hanging around just to run that
experiment on though, which has always been the reason why I can't
simulate this more easily--systems it's prone to happening on aren't cheap.

--
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us