Re: Compression of bigger WAL records

From: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
To: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Cc: pgsql-hackers(at)lists(dot)postgresql(dot)org, Michael Paquier <michael(at)paquier(dot)xyz>, Japin Li <japinli(at)hotmail(dot)com>
Subject: Re: Compression of bigger WAL records
Date: 2026-10-12 21:46:40
Message-ID: CAN4CZFOgbHQFvmBD=To7Hjv1fJ2QMJn0pM-2HcPvH4dqkehxcQ@mail.gmail.com
Views: Whole Thread | Raw Message | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

+/* Compress the assembled record; NULL if that did not pay off */
+static XLogRecData *
+XLogCompressRdt(XLogRecData *rdt)

That doesn't seem to be the case, it only returns NULL on compression
error, incompressible records can get slightly larger with
compression?

Waldump statistics show decompressed totals, is that expected?
Shouldn't we somehow be able to see compressed statistics, maybe
ratios?

While running I can also see numbers like the following with pg_stat_wal

wal_bytes 10 677 687
wal_fpi_bytes 90 204 188

Which seems wrong, as wal_fpi_bytes should be always smaller than wal_bytes?

In response to

Browse pgsql-hackers by date

  From Date Subject
Next Message Greg Burd 2026-10-12 22:00:45 Re: Tepid: selective index updates for heap relations
Previous Message Peter Geoghegan 2026-10-12 21:01:47 Re: index prefetching