Thread

Re: Add wal_fpi_bytes_[un]compressed to pg_stat_wal

Shinya Kato <shinya11.kato@gmail.com> — 2025-10-28T10:33:00Z

On Tue, Oct 28, 2025 at 4:32 PM Michael Paquier <michael@paquier.xyz> wrote:
> Without the changes in instrument.c from patch 0002, patch 0001 that
> implements the basics would not work.  So..  I have moved the changes
> of instrument.c to 0001, reordered the fields to be more consistent,
> did two bumps (catalog, stats file), simplified the docs, then applied
> the result.

Sorry for the inconvenience, and thank you for committing. I have
revised patch 0002, which adds wal_fpi_bytes to EXPLAIN (WAL).

> By the way, Kato-san, what do you think about the attached extra
> simplification?  With the FPIs counted in bytes, I don't see much a
> point in passing around the number of FPIs generated from
> XLogRecordAssemble() to XLogInsertRecord() .

I investigated previous discussions and found [0]. This thread
mentioned that XLogInsert() calls XLogRecordAssemble() multiple times
in its do-while loop, so the value might be invalid.

Based on the discussion above, it seems my previous patch also has the
same issue.

[0] https://www.postgresql.org/message-id/20200329121944.GA79261%40nol

-- 
Best regards,
Shinya Kato
NTT OSS Center