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

Here are some review comments for v54-0001

======
src/backend/replication/slot.c

1.
+ if (*invalidated && SlotIsLogical(s) && IsBinaryUpgrade)
+ {
+ ereport(ERROR,
+ errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("replication slots must not be invalidated during the upgrade"),
+ errhint("\"max_slot_wal_keep_size\" must not be set to -1 during the
upgrade"));
+ }

This new error is replacing the old code:
+ Assert(max_slot_wal_keep_size_mb == -1);

Is that errhint correct? Shouldn't it say "must" instead of "must not"?

======
src/bin/pg_upgrade/t/003_upgrade_logical_replication_slots.pl

2. General formating

Some of the "]);" formatting and indenting for the multiple SQL
commands is inconsistent.

For example,

+ $old_publisher->safe_psql(
+ 'postgres', qq[
+ SELECT pg_create_logical_replication_slot('test_slot1', 'test_decoding');
+ SELECT pg_create_logical_replication_slot('test_slot2', 'test_decoding');
+ ]
+ );

versus

+ $old_publisher->safe_psql(
+ 'postgres', qq[
+ CREATE TABLE tbl AS SELECT generate_series(1, 10) AS a;
+ SELECT pg_replication_slot_advance('test_slot2', NULL);
+ SELECT count(*) FROM pg_logical_emit_message('false', 'prefix',
'This is a non-transactional message');
+ ]);

~~~

3.
+# Set up some settings for the old cluster, so that we can ensures that initdb
+# will be done.
+my @initdb_params = ();
+push @initdb_params, ('--encoding', 'UTF-8');
+push @initdb_params, ('--locale', 'C');
+$node_params{extra} = \(at)initdb_params;
+
+$old_publisher->init(%node_params);

Why would initdb not be done if these were not set? I didn't
understand the comment.

/so that we can ensures/to ensure/

~~~

4.
+# XXX: For PG9.6 and prior, the TAP Cluster.pm assigns 'max_wal_senders' and
+# 'max_connections' to the same value (10). But these versions considered
+# max_wal_senders as a subset of max_connections, so setting the same value
+# will fail. This adjustment will not be needed when packages for older
+#versions are defined.
+if ($old_publisher->pg_version->major <= 9.6)
+{
+ $old_publisher->append_conf(
+ 'postgresql.conf', qq[
+ max_wal_senders = 5
+ max_connections = 10
+ ]);
+}

4a.
IMO remove the complicated comment trying to explain the problem and
just to unconditionally set the values you want.

SUGGESTION#1
# Older PG version had different rules for the inter-dependency of
'max_wal_senders' and 'max_connections',
# so assign values which will work for all PG versions.
$old_publisher->append_conf(
'postgresql.conf', qq[
max_wal_senders = 5
max_connections = 10
]);

~~

4b.
If you really want to put special code here then I think the comment
needs to be more descriptive like below. IMO this suggestion is
overkill, #4a above is much simpler.

SUGGESTION#2
# Versions prior to PG12 considered max_walsenders as a subset
max_connections, so setting the same value will fail.
#
# The TAP Cluster.pm assigns default 'max_wal_senders' and
'max_connections' as follows:
# PG_11: 'max_wal_senders=5' and 'max_connections=10'
# PG_10: 'max_wal_senders=5' and 'max_connections=10'
# Everything else: 'max_wal_senders=10' and 'max_connections=10'
#
# The following code is needed to make adjustments for versions not
already being handled by Cluster.pm.

~

4c.
Alternatively, make necessary adjustments in the Cluster.pm to set
appropriate defaults for all older versions. Then probably you can
remove all this code entirely.

======
Kind Regards,
Peter Smith.
Fujitsu Australia