Horton

Re: WAL usage calculation patch

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Julien Rouhaud <rjuju123@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Fujii Masao <masao.fujii@oss.nttdata.com>, Kirill Bychik <kirill.bychik@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2020-04-27T03:05:51Z
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. 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 Thu, Apr 23, 2020 at 2:35 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Apr 23, 2020 at 12:16 PM Peter Eisentraut
> <peter.eisentraut@2ndquadrant.com> wrote:
>
> >  The internal symbol for the WAL record is
> > XLOG_FPI and xlogdesc.c prints it as "FPI".
> >
>
> That is just one way/reason we log the page.  There are others as
> well.  I thought here we are computing the number of full-page writes
> happened in the system due to various reasons like (a) a page is
> operated upon first time after the checkpoint, (b) log the XLOG_FPI
> record, (c) Guc for WAL consistency checker is on, etc.  If we see in
> XLogRecordAssemble where we decide to log this information, there is a
> comment " .... log a full-page write for the current block." and there
> was an existing variable with 'fpw_lsn' which indicates to an extent
> that what we are computing in this patch is full-page writes.  But
> there is a reference to full-page image as well.  I think as
> full_page_writes is an exposed variable that is well understood so
> exposing information with similar name via this patch doesn't sound
> illogical to me. Whatever we use here we need to be consistent all
> throughout, even pg_stat_statements need to name exposed variable as
> wal_fpi instead of wal_fpw.
>
> To me, full-page writes sound more appealing with other WAL usage
> variables like records and bytes. I might be more used to this term as
> 'fpw' that is why it occurred better to me.  OTOH, if most of us think
> that a full-page image is better suited here, I am fine with changing
> it at all places.
>

Julien, Peter, others do you have any opinion here?  I think it is
better if we decide on one of FPW or FPI and make the changes at all
places for this patch.


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