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 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.

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