RE: [PATCH] Use indexes on the subscriber when REPLICA IDENTITY is full on the publisher

Dear Önder,

Thank you for updating the patch!

> It is not about CREATE INDEX being async. It is about pg_stat_all_indexes
> being async. If we do not wait, the tests become flaky, because sometimes
> the update has not been reflected in the view immediately.

Make sense, I forgot how stats collector works...

Followings are comments for v16. Only for test codes.

~~~
01. 032_subscribe_use_index.pl - SUBSCRIPTION CAN UPDATE THE INDEX IT USES AFTER ANALYZE

```
# show that index_b is not used
$node_subscriber->poll_query_until(
	'postgres', q{select idx_scan=0 from pg_stat_all_indexes where indexrelname = 'index_b';}
) or die "Timed out while waiting for check subscriber tap_sub_rep_full updates two rows via index scan with index on high cardinality column-2";
```

poll_query_until() is still remained here, it should be replaced to is().


02. 032_subscribe_use_index.pl - SUBSCRIPTION BEHAVIOR WITH ENABLE_INDEXSCAN

```
# show that the unique index on replica identity is used even when enable_indexscan=false
$result = $node_subscriber->safe_psql('postgres',
	"select idx_scan from pg_stat_all_indexes where indexrelname = 'test_replica_id_full_idx'");
is($result, qq(0), 'ensure subscriber has not used index with enable_indexscan=false');
```

Is the comment wrong? The index test_replica_id_full_idx is not used here.


032_subscribe_use_index.pl - SUBSCRIPTION CAN UPDATE THE INDEX IT USES AFTER ANALYZE

```
# show that index_b is not used
$node_subscriber->poll_query_until(
	'postgres', q{select idx_scan=0 from pg_stat_all_indexes where indexrelname = 'index_b';}
) or die "Timed out while waiting for check subscriber tap_sub_rep_full updates two rows via index scan with index on high cardinality column-2";
```

poll_query_until() is still remained here, it should be replaced to is()

032_subscribe_use_index.pl - SUBSCRIPTION BEHAVIOR WITH ENABLE_INDEXSCAN

```
# show that the unique index on replica identity is used even when enable_indexscan=false
$result = $node_subscriber->safe_psql('postgres',
	"select idx_scan from pg_stat_all_indexes where indexrelname = 'test_replica_id_full_idx'");
is($result, qq(0), 'ensure subscriber has not used index with enable_indexscan=false');
```

Is the comment wrong? The index test_replica_id_full_idx is not used here.

03. 032_subscribe_use_index.pl - SUBSCRIPTION BEHAVIOR WITH ENABLE_INDEXSCAN

```
$node_publisher->safe_psql('postgres',
	"ALTER TABLE test_replica_id_full REPLICA IDENTITY USING INDEX test_replica_id_full_unique;");
```

I was not sure why ALTER TABLE REPLICA IDENTITY USING INDEX was done on the publisher side.
IIUC this feature works when REPLICA IDENTITY FULL is specified on a publisher,
so it might not be altered here. If so, an index does not have to define on the publisher too.

04. 032_subscribe_use_index.pl - SUBSCRIPTION BEHAVIOR WITH ENABLE_INDEXSCAN

```
$node_subscriber->poll_query_until(
	'postgres', q{select (idx_scan=1) from pg_stat_all_indexes where indexrelname = 'test_replica_id_full_unique'}
) or die "Timed out while waiting ensuring subscriber used unique index as replica identity even with enable_indexscan=false'";
```

03 comment should be added here.


Best Regards,
Hayato Kuroda
FUJITSU LIMITED