Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> My gut feeling is that a reasonable compromise is to set hint bits like
> we do today, but don't mark the page as dirty when only hint bits are
> set. That way you get the benefit of hint bits for tuples that are
> frequently accessed and stay in buffer cache. But you don't spend any
> extra I/O to set them.
I think it's far more likely that that could be acceptable than the
radical method of removing hint bits altogether.
I have not looked into what's wrong with Merlin's test case, but my
thinking about it goes like this: we know that contention for buffer
lookup is significant at high loads, despite the facts that the accesses
are distributed across a lot of independently-usable buffers and we've
done much work to partition the lookup locks. If we remove hint bits
and thereby force an access to clog for every tuple touch, we can expect
that the contention for clog access will be comparable to the worst case
for buffer access contention ... except that in many cases, it will be
distributed across far fewer pages and so the actual interference rate
will be far higher. This will make our past experiences with "context
swap storms" look like a day at the beach.
regards, tom lane