Re: Synchronizing slots from primary to standby - Mailing list pgsql-hackers

In addition to my recent v35-0001 comment not yet addressed [1], here
are some review comments for patch v37-0001.

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src/backend/replication/walsender.c

1. PhysicalWakeupLogicalWalSnd
+/*
+ * Wake up logical walsenders with failover-enabled slots if the physical slot
+ * of the current walsender is specified in standby_slot_names GUC.
+ */
+void
+PhysicalWakeupLogicalWalSnd(void)
+{
+ ListCell   *lc;
+ List    *standby_slots;
+ bool slot_in_list = false;
+
+ Assert(MyReplicationSlot != NULL);
+ Assert(SlotIsPhysical(MyReplicationSlot));
+
+ standby_slots = GetStandbySlotList(false);
+
+ foreach(lc, standby_slots)
+ {
+ char    *name = lfirst(lc);
+
+ if (strcmp(name, NameStr(MyReplicationSlot->data.name)) == 0)
+ {
+ slot_in_list = true;
+ break;
+ }
+ }
+
+ if (slot_in_list)
+ ConditionVariableBroadcast(&WalSndCtl->wal_confirm_rcv_cv);
+}

1a.
Easier to have single assertion -- Assert(MyReplicationSlot &&
SlotIsPhysical(MyReplicationSlot));

~

1b.
Why bother with the 'slot_in_list' and break, when you can just call
the ConditionVariableBroadcast() and return without having the extra
variable?

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src/test/recovery/t/050_verify_slot_order.pl

~~~

2.
Should you name the global objects with a 'regress_' prefix which
seems to be the standard for other new TAP tests?

~~~

3.
+#
+#            | ----> standby1 (connected via streaming replication)
+# | ----> standby2 (connected via streaming replication)
+# primary ----- |
+#     | ----> subscriber1 (connected via logical replication)
+#     | ----> subscriber2 (connected via logical replication)
+#
+#
+# Set up is configured in such a way that primary never lets subscriber1 ahead
+# of standby1.

3a.
Misaligned "|" in comment?

~

3b.
IMO it would be better to give an overview of how this all works
instead of just saying "configured in such a way".


~~~

4.
+# Configure primary to disallow specified logical replication slot (lsub1_slot)
+# getting ahead of specified physical replication slot (sb1_slot).
+$primary->append_conf(

It is confusing because there is no "lsub1_slot" specified anywhere
until much later. Would you be able to provide some more details?

~~~

5.
+# Create another subscriber node, wait for sync to complete
+my $subscriber2 = PostgreSQL::Test::Cluster->new('subscriber2');
+$subscriber2->init(allows_streaming => 'logical');
+$subscriber2->start;
+$subscriber2->safe_psql('postgres', "CREATE TABLE tab_int (a int
PRIMARY KEY);");
+$subscriber2->safe_psql('postgres',
+ "CREATE SUBSCRIPTION mysub2 CONNECTION '$publisher_connstr' "
+   . "PUBLICATION mypub WITH (slot_name = lsub2_slot);");
+$subscriber2->wait_for_subscription_sync;

Maybe this comment should explicitly say there is no failover enabled
here. Maybe the SUBSCRIPTION should explicitly set failover=false?

~~~

6.
+# The subscription that's up and running and is enabled for failover
+# doesn't get the data from primary and keeps waiting for the
+# standby specified in standby_slot_names.
+$result = $subscriber1->safe_psql('postgres',
+ "SELECT count(*) = 0 FROM tab_int;");
+is($result, 't', "subscriber1 doesn't get data from primary until
standby1 acknowledges changes");

Might it be better to write as "SELECT count(*) = $primary_row_count
FROM tab_int;" and expect it to return false?

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src/test/regress/expected/subscription.out

7.
Everything here displays the "Failover" state 'd' (disabled). How
about tests for different state values?

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[1] https://www.postgresql.org/message-id/CAHut%2BPv-yu71ogj_hRi6cCtmD55bsyw7XTxj1Nq8yVFKpY3NDQ%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia