Horton

Re: SLRU statistics

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tomas Vondra <tomas.vondra@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: 2020-02-28T23:19:18Z
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:

On 2020-Jan-21, Tomas Vondra wrote:

> On Tue, Jan 21, 2020 at 05:09:33PM +0900, Masahiko Sawada wrote:

> > I've not tested the performance impact but perhaps we might want to
> > disable these counter by default and controlled by a GUC. And similar
> > to buffer statistics it might be better to inline
> > pgstat_count_slru_page_xxx function for better performance.
> 
> Hmmm, yeah. Inlining seems like a good idea, and maybe we should have
> something like track_slru GUC.

I disagree with adding a GUC.  If a performance impact can be measured
let's turn the functions to static inline, as already proposed.  My
guess is that pgstat_count_slru_page_hit() is the only candidate for
that; all the other paths involve I/O or lock acquisition or even WAL
generation, so the impact won't be measurable anyhow.  We removed
track-enabling GUCs years ago.

BTW, this comment:
			/* update the stats counter of pages found in shared buffers */

is not strictly true, because we don't use what we normally call "shared
buffers"  for SLRUs.

Patch applies cleanly.  I suggest to move the page_miss() call until
after SlruRecentlyUsed(), for consistency with the other case.

I find SlruType pretty odd, and the accompanying "if" list in
pg_stat_get_slru() correspondingly so.  Would it be possible to have
each SLRU enumerate itself somehow?  Maybe add the name in SlruCtlData
and query that, somehow.  (I don't think we have an array of SlruCtlData
anywhere though, so this might be a useless idea.)

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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