Re: speed up a logical replica setup

On Mon, Jan 1, 2024, at 7:14 AM, vignesh C wrote:
> 1) This Assert can fail if source is shutdown:
> +static void
> +drop_replication_slot(PGconn *conn, LogicalRepInfo *dbinfo, const
> char *slot_name)
> +{
> + PQExpBuffer str = createPQExpBuffer();
> + PGresult *res;
> +
> + Assert(conn != NULL);

Oops. I'll remove it.

> 2) Should we have some checks to see if the max replication slot
> configuration is ok based on the number of slots that will be created,
> we have similar checks in upgrade replication slots in
> check_new_cluster_logical_replication_slots

That's a good idea.

> 3) Should we check if wal_level is set to logical, we have similar
> checks in upgrade replication slots in
> check_new_cluster_logical_replication_slots

That's a good idea.

> 4) The physical replication slot that was created will still be
> present in the primary node, I felt this should be removed.

My proposal is to remove it [1]. It'll be include in the next version.

> 5) I felt the target server should be started before completion of
> pg_subscriber:

Why? The initial version had an option to stop the subscriber. I decided to
remove the option and stop the subscriber by default mainly because (1) it is
an extra step to start the server (another point is that the WAL retention
doesn't happen due to additional (synchronized?) replication slots on
subscriber -- point 2). It was a conservative choice. If point 2 isn't an
issue, imo point 1 is no big deal.

[1] https://www.postgresql.org/message-id/e02a2c17-22e5-4ba6-b788-de696ab74f1e%40app.fastmail.com

--
Euler Taveira
EDB https://www.enterprisedb.com/