Re: Design notes for BufMgrLock rewrite

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Tom Lane wrote:
>> One thing I realized quickly is that there is no natural way in a clock
>> algorithm to discourage VACUUM from blowing out the cache.  I came up
>> with a slightly ugly idea that's described below.  Can anyone do better?

> Uh, is the clock algorithm also sequential-scan proof?  Is that
> something that needs to be done too?

If you can think of a way.  I don't see any way to make the algorithm
itself scan-proof, but if we modified the bufmgr API to tell ReadBuffer
(or better ReleaseBuffer) that a request came from a seqscan, we could
do the same thing as for VACUUM.  Whether that's good enough isn't
clear --- for one thing it would kick up the contention for the
BufFreelistLock, and for another it might mean *too* short a lifetime
for blocks fetched by seqscan.
        regards, tom lane