Re: Design notes for BufMgrLock rewrite

Tom Lane wrote:
> "Jim C. Nasby" <decibel@decibel.org> writes:
> 
>>The advantage of using a counter instead of a simple active
>>bit is that buffers that are (or have been) used heavily will be able to
>>go through several sweeps of the clock before being freed. Infrequently
>>used buffers (such as those from a vacuum or seq.  scan), would get
>>marked as inactive the first time they were hit by the clock hand.

> What I'm envisioning is that pinning (actually unpinning) a buffer
> increments the counter (up to some limit), and the clock sweep
> decrements it (down to zero), and only buffers with count zero are taken
> by the sweep for recycling.

Would there be any value in incrementing by 2 for index accesses and 1 
for seq-scans/vacuums? Actually, it should probably be a ratio based on 
random_page_cost shouldn't it?

--   Richard Huxton  Archonet Ltd