Re: Synchronizing slots from primary to standby

Hi,

On Fri, Mar 01, 2024 at 03:22:55PM +1100, Peter Smith wrote:
> Here are some review comments for v102-0001.
>
> ======
> doc/src/sgml/config.sgml
>
> 1.
> + <para>
> + Lists the streaming replication standby server slot names that logical
> + WAL sender processes will wait for. Logical WAL sender processes will
> + send decoded changes to plugins only after the specified replication
> + slots confirm receiving WAL. This guarantees that logical replication
> + slots with failover enabled do not consume changes until those changes
> + are received and flushed to corresponding physical standbys. If a
> + logical replication connection is meant to switch to a physical standby
> + after the standby is promoted, the physical replication slot for the
> + standby should be listed here. Note that logical replication will not
> + proceed if the slots specified in the standby_slot_names do
> not exist or
> + are invalidated.
> + </para>
>
> Should this also mention the effect this GUC has on those 2 SQL
> functions? E.g. Commit message says:
>
> Additionally, The SQL functions pg_logical_slot_get_changes and
> pg_replication_slot_advance are modified to wait for the replication
> slots mentioned in 'standby_slot_names' to catch up before returning.

I think that's also true for all the ones that rely on
pg_logical_slot_get_changes_guts(), means:

- pg_logical_slot_get_changes
- pg_logical_slot_peek_changes
- pg_logical_slot_get_binary_changes
- pg_logical_slot_peek_binary_changes

Not sure it's worth to mention the "binary" ones though as their doc mention
they behave as their "non binary" counterpart.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com