RE: SLRU statistics

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
> You're right the users can't really take advantage of this - my primary
> motivation was providing a feedback for devs, benchmarking etc. That
> might have been done with DEBUG messages or something, but this seems
> more convenient.

Understood. I'm in favor of adding performance information even if it doesn't make sense for users (like other DBMSs sometimes do.) One concern is that all the PostgreSQL performance statistics have been useful so far for tuning in some way, and this may become the first exception. Do we describe the SLRU stats view in the manual, or hide it only for PG devs and support staff?

> I think it's unclear how desirable / necessary it is to allow users to
> tweak those caches. I don't think we should have a GUC for everything,
> but maybe there's some sort of heuristics to determine the size. The
> assumption is we actually find practical workloads where the size of
> these SLRUs is a performance issue.

I understood that the new performance statistics are expected to reveal what SLRUs need to be tunable and/or implemented with a different mechanism like shared buffers.

Regards
Takayuki Tsunakawa