| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, shveta malik <shveta(dot)malik(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Shlok Kyal <shlok(dot)kyal(dot)oss(at)gmail(dot)com>, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: POC: enable logical decoding when wal_level = 'replica' without a server restart |
| Date: | 2026-02-15 17:31:17 |
| Message-ID: | auqtlnoea5qmg2kxkdiumvi24dhfd4jdf2yqhgpvkou7kdxs2n@vsofxuejplqh |
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| Lists: | pgsql-hackers |
Hi,
On 2026-02-15 18:18:30 +0100, Matthias van de Meent wrote:
> However, with the current code, the DBA can't make the choice whether
> to allow logical replication or not, at least not without reverting to
> wal_level=minimal -- which removes effectively all HA features. No
> amount of monitoring or rights management can make a DBA safely use
> the features enabled by wal_level=replica without risking additional
> overhead with effective_wal_level=logical; a very significant change
> from PG versions up to 18, where you could safely run your server like
> that.
I really don't understand this argument. If you are worried about WAL volume:
Any user with rights to create a table or do DML can increase WAL volume to an
arbitrary degree. And that's actually harder to pinpoint than seeing that a
new replication slot has been created, since the user creating a lot of WAL
with a new table can do so in a transaction that creates and drops the table,
thereby never having any visible stats.
What is the realistic scenario in which you trust a user enough to have
REPLICATION rights, i.e. a right to read *all* data in the server *and* to
hold back horizons arbitrarily far, but you are worried about them creating
logical replication slots? I don't think it exists.
Greetings,
Andres Freund
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