Re: [HACKERS] logical decoding of two-phase transactions

On Tue, Jul 27, 2021 at 11:41 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> Please find attached the latest patch set v99*
>
> v98-0001 --> split into v99-0001 + v99-0002
>

Pushed the first refactoring patch after making few modifications as below.
1.
- /* open the spool file for the committed transaction */
+ /* Open the spool file for the committed/prepared transaction */
changes_filename(path, MyLogicalRepWorker->subid, xid);

In the above comment, we don't need to say prepared. It can be done as
part of the second patch.

2.
+apply_handle_prepare_internal(LogicalRepPreparedTxnData
*prepare_data, char *gid)

I don't think there is any need for this function to take gid as
input. It can compute by itself instead of callers doing it.

3.
+static TransactionId+logicalrep_read_prepare_common(StringInfo in,
char *msgtype,
+ LogicalRepPreparedTxnData *prepare_data)

I don't think the above function needs to return xid because it is
already present as part of prepare_data. Even, if it is required due
to some reason for the second patch then let's do it as part of if but
I don't think it is required for the second patch.

4.
/*
- * Write PREPARE to the output stream.
+ * Common code for logicalrep_write_prepare and
logicalrep_write_stream_prepare.
*/

Here and at a similar another place, we don't need to refer to
logicalrep_write_stream_prepare as that is part of the second patch.

Few comments on 0002 patch:
==========================
1.
+# ---------------------
+# 2PC + STREAMING TESTS
+# ---------------------
+
+# Setup logical replication (streaming = on)
+
+$node_B->safe_psql('postgres', "
+ ALTER SUBSCRIPTION tap_sub_B
+ SET (streaming = on);");
+
+$node_C->safe_psql('postgres', "
+ ALTER SUBSCRIPTION tap_sub_C
+ SET (streaming = on)");
+
+# Wait for subscribers to finish initialization
+$node_A->wait_for_catchup($appname_B);
+$node_B->wait_for_catchup($appname_C);

This is not the right way to determine if the new streaming option is
enabled on the publisher. Even if there is no restart of apply workers
(and walsender) after you have enabled the option, the above wait will
succeed. You need to do something like below as we are doing in
001_rep_changes.pl:

$oldpid = $node_publisher->safe_psql('postgres',
"SELECT pid FROM pg_stat_replication WHERE application_name = 'tap_sub';"
);
$node_subscriber->safe_psql('postgres',
"ALTER SUBSCRIPTION tap_sub SET PUBLICATION tap_pub_ins_only WITH
(copy_data = false)"
);
$node_publisher->poll_query_until('postgres',
"SELECT pid != $oldpid FROM pg_stat_replication WHERE application_name
= 'tap_sub';"
) or die "Timed out while waiting for apply to restart";

2.
+# Create some pre-existing content on publisher (uses same DDL as
015_stream test)

Here, in the comments, I don't see the need to same uses same DDL ...

--
With Regards,
Amit Kapila.