Re: Placement of synchronized_standby_slots description in config.sgml

On Fri, Jan 23, 2026 at 7:22 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
> Hi,
>
> synchronized_standby_slots is defined in guc_parameter.dat as part of
> the REPLICATION_PRIMARY group and appears under the "Primary Server"
> section in postgresql.conf.sample. However, in the documentation
> its description is placed under the "Sending Servers" section.
>
> Given this, it seems the description should also be under "Primary Server"
> in the documentation. I've attached a patch that moves it there.

Thank you for the patch! The patch LGTM.

> Alternatively, if synchronized_standby_slots is intended to be set also
> on a standby in cascading replication setups, then the current documentation
> placement may be correct, and instead guc_parameter.dat and
> postgresql.conf.sample should be updated. My understanding, though,
> is that this parameter is normally set only on the primary. Right?

You're right. PhysicalWakeupLogicalWalSnd() in walsender.c has this check:

/*
* If we are running in a standby, there is no need to wake up walsenders.
* This is because we do not support syncing slots to cascading standbys,
* so, there are no walsenders waiting for standbys to catch up.
*/
if (RecoveryInProgress())
return;

So this parameter is only meaningful on the primary.

--
Best regards,
Shinya Kato
NTT OSS Center