Horton

Re: WAL usage calculation patch

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Fujii Masao <masao.fujii@oss.nttdata.com>, Kirill Bychik <kirill.bychik@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2020-04-04T09:09:32Z
Lists: pgsql-hackers

Commits

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  1. Change the display of WAL usage statistics in Explain.

  2. Cosmetic fixups for WAL usage work.

  3. Allow parallel create index to accumulate buffer usage stats.

  4. Allow autovacuum to log WAL usage statistics.

  5. Add the option to report WAL usage in EXPLAIN and auto_explain.

  6. Allow pg_stat_statements to track WAL usage statistics.

  7. Add infrastructure to track WAL usage.

  8. Include information on buffer usage during planning phase, in EXPLAIN output, take two.

  9. Include information on buffer usage during planning phase, in EXPLAIN output.

  10. Allow parallel vacuum to accumulate buffer usage.

  11. Allow pg_stat_statements to track planning statistics.

On Sat, Apr 4, 2020 at 2:24 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
> >
> > We can add if we want but I am not able to convince myself for that.
> > Do you have any use case in mind?  I think in most of the cases
> > (except for hint-bit WAL) it will be zero. If we are not sure of this
> > we can also discuss it separately in a new thread once this
> > patch-series is committed and see if anybody else sees the value of it
> > and if so adding the code should be easy.
>
>
> I'm mostly thinking of people trying to investigate possible slowdowns on a
> hot-standby replica with a primary without wal_log_hints.  If they explicitly
> ask for WAL information, we should provide them, even if it's quite unlikely to
> happen.
>

Yeah, possible but I am not completely sure.  I would like to hear the
opinion of others if any before adding code for this.  How about if we
first commit pg_stat_statements and wait for this till Monday and if
nobody responds we can commit the current patch but would start a new
thread and try to get the opinion of others?

>
> >
> > >  I'm wondering how stable the normalized
> > > WAL information would be in some regression tests, as the counters are only
> > > showed if non zero.  Maybe it'd be better to remove them from the output, same
> > > as the buffers?
> > >
> >
> > Which regression tests are you referring to? pg_stat_statements?  If
> > so, why would it be unstable?  It should always generate WAL although
> > the exact values may differ and we have already taken care of that in
> > the patch, no?
>
>
> I'm talking about a hypothetical new EXPLAIN (ALAYZE, WAL) regression test,
> which could be unstable for similar reason to why the first attempt to add
> BUFFERS in the planning part of EXPLAIN was unstable.
>

oh, then leave it for now because I don't see much use of those as the
code path can anyway be hit by the tests added by pg_stat_statements
patch.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com