Re: Minimal logical decoding on standbys

> From 56a9559555918a99c202a0924f7b2ede9de4e75d Mon Sep 17 00:00:00 2001
> From: bdrouvotAWS <bdrouvot(at)amazon(dot)com>
> Date: Tue, 7 Feb 2023 08:59:47 +0000
> Subject: [PATCH v52 3/6] Allow logical decoding on standby.
>
> Allow a logical slot to be created on standby. Restrict its usage
> or its creation if wal_level on primary is less than logical.
> During slot creation, it's restart_lsn is set to the last replayed
> LSN. Effectively, a logical slot creation on standby waits for an
> xl_running_xact record to arrive from primary.

Hmm, not sure if it really applies here, but this sounds similar to
issues with track_commit_timestamps: namely, if the primary has it
enabled and you start a standby with it enabled, that's fine; but if the
primary is later shut down (but the standby isn't) and then the primary
restarted with a lesser value, then the standby would misbehave without
any obvious errors. If that is a real problem, then perhaps you can
solve it by copying some of the logic from track_commit_timestamps,
which took a large number of iterations to get right.

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Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"No hay ausente sin culpa ni presente sin disculpa" (Prov. francés)