Re: pg_buffercache's usage count

On Feb 24, 2010, at 11:09 AM, Greg Smith wrote:

> 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
acrossa data set and application with a repeatable benchmark where most of the data ends up at 5, but there's still a
lotof buffer cache churn, to allow testing whether a further increase could be valuable.  So far nobody has actually
foundsuch 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
alwaysbeen the reason why I can't simulate this more easily--systems it's prone to happening on aren't cheap. 


Well as it happens we *did* just get our third slony node in today, and it could spend some time doing burn-in
experimentsif it would be helpful. Unfortunately, I won't be able to drive the same load against it, so I don't know
howuseful it would be.