Clean-ups for 776621a5e4 and 7329240437.

Following are a few clean-ups related to failover option support in slots:
1. Improve the documentation in create_subscription.sgml.
2. Remove the spurious blank line in subscriptioncmds.c.
3. Remove the NOTICE for alter_replication_slot in subscriptioncmds.c as
we would sometimes print it even when nothing has changed. One can find
the change by enabling log_replication_commands on the publisher.
4. Optimize ReplicationSlotAlter() function to prevent disk flushing when
the slot's data remains unchanged.

Author: Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/[email protected]
Discussion: https://postgr.es/m/OS0PR01MB57164904651FB588A518E98894472@OS0PR01MB5716.jpnprd01.prod.outlook.com

2 files changed, 9 insertions, 13 deletions

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index a400ba0e40c..a05d69922d9 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,7 +73,6 @@
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
 
-
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
 
@@ -852,9 +851,6 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
 				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
-				ereport(NOTICE,
-						(errmsg("changed the failover state of replication slot \"%s\" on publisher to %s",
-								opts.slot_name, opts.failover ? "true" : "false")));
 			}
 		}
 		PG_FINALLY();
@@ -1547,10 +1543,6 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		PG_TRY();
 		{
 			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
-
-			ereport(NOTICE,
-					(errmsg("changed the failover state of replication slot \"%s\" on publisher to %s",
-							sub->slotname, opts.failover ? "true" : "false")));
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 110cb59783f..fd4e96c9d69 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -696,12 +696,16 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errmsg("cannot use %s with a physical replication slot",
 					   "ALTER_REPLICATION_SLOT"));
 
-	SpinLockAcquire(&MyReplicationSlot->mutex);
-	MyReplicationSlot->data.failover = failover;
-	SpinLockRelease(&MyReplicationSlot->mutex);
+	if (MyReplicationSlot->data.failover != failover)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.failover = failover;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		ReplicationSlotMarkDirty();
+		ReplicationSlotSave();
+	}
 
-	ReplicationSlotMarkDirty();
-	ReplicationSlotSave();
 	ReplicationSlotRelease();
 }