Horton

Re: SLRU statistics

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>, "tsunakawa.takay@fujitsu.com" <tsunakawa.takay@fujitsu.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-03-28T00:26:30Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix async.c to not register any SLRU stats counts in the postmaster.

  2. Use proper GetDatum function in pg_stat_get_slru().

  3. Initialize SLRU stats entries to zero.

  4. Remove pg_xact from pg_stat_reset_slru docs

  5. Remove pg_xact entry from SLRU stats

  6. Track SLRU page hits in SimpleLruReadPage_ReadOnly

  7. Fix typo in SLRU stats documentation

  8. Collect statistics about SLRU caches

  9. Simplify and rename some GUC variables, per various recent discussions:

Attachments

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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