Re: WIP: 2nd-generation buffer ring patch

I wrote:
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
>> If there's no easy solution, I think we could live
>> with that, but Greg's suggestion of bumping the usage_count in PinBuffer
>> instead of UnpinBuffer sounds like a nice solution to me.

> After thinking about it more, I'm a bit hesitant to do that because it
> will change the interaction with the clock sweep for buffers that stay
> pinned for awhile. I had suggested making the clock sweep not decrement
> usage_count of a pinned buffer, but I think that would change the
> fairness of the algorithm. OTOH it may not matter that much if we just
> move the usage_count increment and leave the clock sweep alone. Do we
> have any decent way of measuring the effectiveness of the clock-sweep
> allocation algorithm?

Despite above misgivings, here's a version of the patch that moves
usage_count incrementing to PinBuffer instead of UnpinBuffer. It does
seem a good bit cleaner.

regards, tom lane