Re: SLRU statistics

Hi,

here is a bit improved version of the patch - I've been annoyed by how
the resetting works (per-entry timestamp, but resetting all entries) so
I've added a new function pg_stat_reset_slru() that allows resetting
either all entries or just one entry (identified by name). So

SELECT pg_stat_reset_slru('clog');

resets just "clog" SLRU counters, while

SELECT pg_stat_reset_slru(NULL);

resets all entries.

I've also done a bit of benchmarking, to see if this has measurable
impact (in which case it might deserve a new GUC), and I think it's not
measurable. I've used a tiny unlogged table (single row).

CREATE UNLOGGED TABLE t (a int);
INSERT INTO t VALUES (1);

and then short pgbench runs with a single client, updatint the row. I've
been unable to measure any regression, it's all well within 1% so noise.
But perhaps there's some other benchmark that I should do?

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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