Re: WAL usage calculation patch

On Mon, Feb 10, 2020 at 8:20 PM Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On Wed, 5 Feb 2020 at 21:36, Kirill Bychik <kirill(dot)bychik(at)gmail(dot)com> wrote:
> > Patch is separated in two parts: core changes and pg_stat_statements
> > additions. Essentially the extension has its schema updated to allow
> > two more fields, docs updated to reflect the change. Patch is prepared
> > against master branch.
> >
> > Please provide your comments and/or code findings.
>
> I like the concept, I'm a big fan of anything that affordably improves
> visibility into Pg's I/O and activity.

+1

> To date I've been relying on tools like systemtap to do this sort of
> thing. But that's a bit specialised, and Pg currently lacks useful
> instrumentation for it so it can be a pain to match up activity by
> parallel workers and that sort of thing. (I aim to find time to submit
> a patch for that.)

(I'm interested in seeing your conference talk about that! I did a
bunch of stuff with static probes to measure PHJ behaviour around
barrier waits and so on but it was hard to figure out what stuff like
that to put in the actual tree, it was all a bit
use-once-to-test-a-theory-and-then-throw-away.)

Kirill, I noticed that you included a regression test that is failing. Can
this possibly be stable across machines or even on the same machine?
Does it still pass for you or did something change on the master
branch to add a new WAL record since you posted the patch?

query | calls | rows | wal_write_bytes | wal_write_records
-------------------------------------------+-------+------+-----------------+-------------------
- CREATE INDEX test_b ON test(b) | 1 | 0 | 1673 |
16
- DROP FUNCTION IF EXISTS PLUS_ONE(INTEGER) | 1 | 0 | 56 |
1
+ CREATE INDEX test_b ON test(b) | 1 | 0 | 1755 |
17
+ DROP FUNCTION IF EXISTS PLUS_ONE(INTEGER) | 1 | 0 | 0 |
0