Re: [PoC] pg_upgrade: allow to upgrade publisher node

Hi Kuroda-san.

I already posted a review for v22-0003 earlier today, but v23-0003 was
already posted so those are not yet addressed.

Here are a few more review comments I noticed when looking at the latest
v23-0003.

======
src/bin/pg_upgrade/check.c

1.
+#include "access/xlogdefs.h"
#include "catalog/pg_authid_d.h"

Was this #include needed here? I noticed you've already included the same
in the "pg_upgrade.h".

~~~

2. check_for_lost_slots

+ /* Check there are no logical replication slots with a 'lost' state. */
+ res = executeQueryOrDie(conn,
+ "SELECT slot_name FROM pg_catalog.pg_replication_slots "
+ "WHERE wal_status = 'lost' AND "
+ "temporary IS FALSE;");

I can't quite describe my doubts about this, but something seems a bit
strange. Didn't we already iterate every single slot in all DBs in the
earlier function get_logical_slot_infos_per_db()? There we were only
looking for wal_status <> 'lost', but we could have got *every* wal_status
and also detected these 'lost' ones at the same time up-front, instead of
having this extra function with more SQL to do pretty much the same SELECT.

Perhaps coding the current way there is a clear separation of the fetching
code and the checking code, and that might be the best approach, but it
somehow seems a shame/waste to be executing almost the same slots data with
the same SQL 2x, so I wondered if there is a better way to arrange this.

======
src/bin/pg_upgrade/info.c

3. get_logical_slot_infos

+
+ /* Do additional checks if slots are found */
+ if (slot_count)
+ {
+ check_for_lost_slots(cluster);
+
+ if (!live_check)
+ check_for_confirmed_flush_lsn(cluster);
+ }

Aren't these checks only intended for checking the 'old_cluster'? But
AFAICT they are not guarded here so they will be executed by both sides.
Previously (in my review of v22-0003) I suggested these calls maybe
belonged in the calling function check_and_dump_old_cluster(). I think that.

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Kind Regards,
Peter Smith.
Fujitsu Australia