Re: Synchronizing slots from primary to standby

On Sat, Mar 2, 2024 at 9:21 AM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> Apart from the comments, the code in WalSndWaitForWal was refactored
> a bit to make it neater. Thanks Shveta for helping writing the code and doc.
>

A few more comments:
==================
1.
+# Wait until the primary server logs a warning indicating that it is waiting
+# for the sb1_slot to catch up.
+$primary->wait_for_log(
+ qr/replication slot \"sb1_slot\" specified in parameter
standby_slot_names does not have active_pid/,
+ $offset);

Shouldn't we wait for such a LOG even in the first test as well which
involves two standbys and two logical subscribers?

2.
+##################################################
+# Test that logical replication will wait for the user-created inactive
+# physical slot to catch up until we remove the slot from standby_slot_names.
+##################################################

I don't see anything different tested in this test from what we
already tested in the first test involving two standbys and two
logical subscribers. Can you please clarify if I am missing something?

3.
Note that after receiving the shutdown signal, an ERROR
+ * is reported if any slots are dropped, invalidated, or inactive. This
+ * measure is taken to prevent the walsender from waiting indefinitely.
+ */
+ if (NeedToWaitForStandby(target_lsn, flushed_lsn, wait_event))

Isn't this part of the comment should be moved inside NeedToWaitForStandby()?

4.
+ /*
+ * Update our idea of the currently flushed position only if we are
+ * not waiting for standbys to catch up, otherwise the standby would
+ * have to catch up to a newer WAL location in each cycle.
+ */
+ if (wait_event != WAIT_EVENT_WAIT_FOR_STANDBY_CONFIRMATION)
+ {

This functionality (in function WalSndWaitForWal()) seems to ensure
that we first wait for the required WAL to be flushed and then wait
for standbys. If true, we should cover that point in the comments here
or somewhere in the function WalSndWaitForWal().

Apart from this, I have made a few modifications in the comments.

--
With Regards,
Amit Kapila.