From 7c3fb505b14e86581b6a052075a294c78c91b123 Mon Sep 17 00:00:00 2001
From: Amit Kapila
Date: Tue, 21 Nov 2023 07:59:53 +0530
Subject: Log messages for replication slot acquisition and release.

This commit log messages (at LOG level when log_replication_commands is
set, otherwise at DEBUG1 level) when walsenders acquire and release
replication slots. These messages help to know the lifetime of a
replication slot - one can know how long a streaming standby, logical
subscriber, or replication slot consumer is down. These messages will be
useful on production servers to debug and analyze inactive replication
slots.

Note that these messages are emitted only for walsenders but not for
backends. This is because walsenders are the ones that typically hold
replication slots for longer durations, unlike backends which hold them
for executing replication related functions.

Author: Bharath Rupireddy
Reviewed-by: Peter Smith, Amit Kapila, Alvaro Herrera
Discussion: http://postgr.es/m/CALj2ACX17G7F-jeLt+7KhJ6YxVeRwR8Zk0rDh4VnT546o0UpTQ@mail.gmail.com
---
 src/backend/replication/slot.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

(limited to 'src')

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 781aa43cc4f..18bc28195b0 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -537,6 +537,16 @@ retry:
 	 */
 	if (SlotIsLogical(s))
 		pgstat_acquire_replslot(s);
+
+	if (am_walsender)
+	{
+		ereport(log_replication_commands ? LOG : DEBUG1,
+				SlotIsLogical(s)
+				? errmsg("acquired logical replication slot \"%s\"",
+						 NameStr(s->data.name))
+				: errmsg("acquired physical replication slot \"%s\"",
+						 NameStr(s->data.name)));
+	}
 }
 
 /*
@@ -549,9 +559,17 @@ void
 ReplicationSlotRelease(void)
 {
 	ReplicationSlot *slot = MyReplicationSlot;
+	char	   *slotname = NULL;	/* keep compiler quiet */
+	bool		is_logical = false; /* keep compiler quiet */
 
 	Assert(slot != NULL && slot->active_pid != 0);
 
+	if (am_walsender)
+	{
+		slotname = pstrdup(NameStr(slot->data.name));
+		is_logical = SlotIsLogical(slot);
+	}
+
 	if (slot->data.persistency == RS_EPHEMERAL)
 	{
 		/*
@@ -596,6 +614,18 @@ ReplicationSlotRelease(void)
 	MyProc->statusFlags &= ~PROC_IN_LOGICAL_DECODING;
 	ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
 	LWLockRelease(ProcArrayLock);
+
+	if (am_walsender)
+	{
+		ereport(log_replication_commands ? LOG : DEBUG1,
+				is_logical
+				? errmsg("released logical replication slot \"%s\"",
+						 slotname)
+				: errmsg("released physical replication slot \"%s\"",
+						 slotname));
+
+		pfree(slotname);
+	}
 }
 
 /*
-- 
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