Re: Add a perl function in Cluster.pm to generate WAL

On Thu, Jun 15, 2023 at 01:40:15PM +0900, Kyotaro Horiguchi wrote:
> +			"CREATE TABLE tt (); DROP TABLE tt; SELECT pg_switch_wal();");
> 
> At least since 11, we can utilize pg_logical_emit_message() for this
> purpose. It's more lightweight and seems appropriate, not only because
> it doesn't cause any side effects but also bacause we don't have to
> worry about name conflicts.

Making this as cheap as possible by design is a good concept for a
common routine.  +1.

> -		 SELECT 'finished';",
> -		timeout => $PostgreSQL::Test::Utils::timeout_default));
> -is($result[1], 'finished', 'check if checkpoint command is not blocked');
> -
> +$node_primary2->advance_wal(1);
> +$node_primary2->safe_psql('postgres', 'CHECKPOINT;');
> 
> This test anticipates that the checkpoint could get blocked. Shouldn't
> we keep the timeout?

Indeed, this would partially invalidate what's getting tested in light
of 1816a1c6 where we run a secondary command after the checkpoint.  So
the last SELECT should remain around.

> -$node_primary->safe_psql(
> -    'postgres', "create table retain_test(a int);
> -                                     select pg_switch_wal();
> -                                     insert into retain_test values(1);
> -                                     checkpoint;");
> +$node_primary->advance_wal(1);
> +$node_primary->safe_psql('postgres', "checkpoint;");
> 
> The original test generated some WAL after the segment switch, which
> appears to be a significant characteristics of the test.

Still it does not matter for this specific case?  The logical slot has
been already invalidated, so we don't care much about logical changes
in WAL, do we?
--
Michael