v58-0001-Introduce-a-new-GUC-max_conflict_retention_durat.patch

From ced59673bf4b88d3ed80ee250f398412f04f4214 Mon Sep 17 00:00:00 2001
From: Zhijie Hou <houzj.fnst@fujitsu.com>
Date: Wed, 23 Jul 2025 13:38:12 +0800
Subject: [PATCH v58 1/2] Introduce a new GUC 'max_conflict_retention_duration'

This commit introduces a GUC option max_conflict_retention_duration, designed
to prevent excessive accumulation of dead tuples when subscription with
retain_dead_tuples enabled is present and the apply worker cannot catch
up with the publisher's workload.

If the time spent advancing non-removable transaction ID surpasses the
max_conflict_retention_duration threshold, the apply worker would stop retaining
information for conflict detection. The replication slot
pg_conflict_detection.xmin will be set to InvalidTransactionId if all apply
workers associated with the subscription, where retain_dead_tuples is enabled,
confirm that the retention duration exceeded the
max_conflict_retention_duration.

In this patch, a replication slot will not be automatically re-initialized.
Users can disable retain_dead_tuples and re-enable it after confirming that the
replication slot has been dropped. An upcoming patch will include support for
automatic slot re-initialization once at least one apply worker confirms that the
retention duration is within the max_conflict_retention_duration limit.

To monitor worker's conflict retention status, this patch also introduces a new
column 'retain_dead_tuples' in the pg_stat_subscription view. This column
indicates whether the apply worker is effectively retaining conflict
information. The value is set to true only if retain_dead_tuples is enabled
for the associated subscription, and the retention duration for conflict
detection by the apply worker has not exceeded max_conflict_retention_duration.
---
 doc/src/sgml/config.sgml                      |  40 ++++
 doc/src/sgml/monitoring.sgml                  |  13 ++
 src/backend/catalog/system_views.sql          |   3 +-
 src/backend/replication/logical/launcher.c    |  40 +++-
 src/backend/replication/logical/worker.c      | 171 +++++++++++++++++-
 src/backend/utils/misc/guc_tables.c           |  13 ++
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/catalog/pg_proc.dat               |   6 +-
 src/include/replication/logicallauncher.h     |   1 +
 src/include/replication/worker_internal.h     |   3 +
 src/test/regress/expected/rules.out           |   5 +-
 src/test/subscription/t/035_conflicts.pl      |  10 +-
 12 files changed, 280 insertions(+), 26 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 20ccb2d6b54..5a9aee66e3f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5399,6 +5399,46 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-max-conflict-retention-duration" xreflabel="max_conflict_retention_duration">
+      <term><varname>max_conflict_retention_duration</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>max_conflict_retention_duration</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Maximum duration for which each apply worker is allowed to retain the
+        information useful for conflict detection when
+        <literal>retain_dead_tuples</literal> is enabled for the associated
+        subscriptions. The default value is <literal>0</literal>, indicating
+        that the information is retained until it is no longer needed for
+        detection purposes. If this value is specified without units, it is
+        taken as milliseconds.
+       </para>
+       <para>
+        The information useful for conflict detection is no longer retained if
+        all apply workers associated with the subscriptions, where
+        <literal>retain_dead_tuples</literal> is enabled, confirm that the
+        retention duration exceeded the
+        <literal>max_conflict_retention_duration</literal>. To re-enable
+        retention, you can disable <literal>retain_dead_tuples</literal> and
+        re-enable it after confirming this replication slot has been dropped.
+       </para>
+       <para>
+        This option is effective only if a subscription with
+        <literal>retain_dead_tuples</literal> enabled is present, and the
+        associated apply worker is active.
+       </para>
+       <warning>
+        <para>
+         Note that setting a non-zero value for this option could lead to
+         conflict information being removed prematurely, potentially missing
+         some conflict detections.
+        </para>
+       </warning>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 3f4a27a736e..cc8baf97223 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -2114,6 +2114,19 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        sender; NULL for parallel apply workers
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>retain_dead_tuples</structfield> <type>boolean</type>
+      </para>
+      <para>
+       True if <link linkend="sql-createsubscription-params-with-retain-dead-tuples"><literal>retain_dead_tuples</literal></link>
+       is enabled and the duration for which information useful for conflict
+       detection is retained by this apply worker does not exceed
+       <xref linkend="guc-max-conflict-retention-duration"/>; NULL for
+       parallel apply workers and table synchronization workers.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 1b3c5a55882..36928430ff3 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -996,7 +996,8 @@ CREATE VIEW pg_stat_subscription AS
             st.last_msg_send_time,
             st.last_msg_receipt_time,
             st.latest_end_lsn,
-            st.latest_end_time
+            st.latest_end_time,
+            st.retain_dead_tuples
     FROM pg_subscription su
             LEFT JOIN pg_stat_get_subscription(NULL) st
                       ON (st.subid = su.oid);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 37377f7eb63..03aa5b2b7a9 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -23,6 +23,7 @@
 #include "access/tableam.h"
 #include "access/xact.h"
 #include "catalog/pg_subscription.h"
+#include "catalog/pg_subscription_d.h"
 #include "catalog/pg_subscription_rel.h"
 #include "funcapi.h"
 #include "lib/dshash.h"
@@ -43,6 +44,7 @@
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
 #include "utils/snapmgr.h"
+#include "utils/syscache.h"
 
 /* max sleep time between cycles (3min) */
 #define DEFAULT_NAPTIME_PER_CYCLE 180000L
@@ -51,6 +53,7 @@
 int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
 int			max_parallel_apply_workers_per_subscription = 2;
+int			max_conflict_retention_duration = 0;
 
 LogicalRepWorker *MyLogicalRepWorker = NULL;
 
@@ -102,7 +105,7 @@ static void ApplyLauncherSetWorkerStartTime(Oid subid, TimestampTz start_time);
 static TimestampTz ApplyLauncherGetWorkerStartTime(Oid subid);
 static void compute_min_nonremovable_xid(LogicalRepWorker *worker, TransactionId *xmin);
 static bool acquire_conflict_slot_if_exists(void);
-static void advance_conflict_slot_xmin(TransactionId new_xmin);
+static void update_conflict_slot_xmin(TransactionId new_xmin);
 
 
 /*
@@ -1320,13 +1323,18 @@ ApplyLauncherMain(Datum main_arg)
 		 * that requires us to retain dead tuples. Otherwise, if required,
 		 * advance the slot's xmin to protect dead tuples required for the
 		 * conflict detection.
+		 *
+		 * However, if all apply workers for subscriptions with
+		 * retain_dead_tuples enabled have requested to cease retention, the
+		 * new xmin will be set to InvalidTransactionId. We then update
+		 * slot.xmin accordingly to permit the removal of dead tuples.
 		 */
 		if (MyReplicationSlot)
 		{
 			if (!retain_dead_tuples)
 				ReplicationSlotDropAcquired();
 			else if (can_advance_xmin)
-				advance_conflict_slot_xmin(xmin);
+				update_conflict_slot_xmin(xmin);
 		}
 
 		/* Switch back to original memory context. */
@@ -1378,7 +1386,12 @@ compute_min_nonremovable_xid(LogicalRepWorker *worker, TransactionId *xmin)
 	nonremovable_xid = worker->oldest_nonremovable_xid;
 	SpinLockRelease(&worker->relmutex);
 
-	Assert(TransactionIdIsValid(nonremovable_xid));
+	/*
+	 * Skip collecting oldest_nonremovable_xid for workers that have stopped
+	 * conflict retention.
+	 */
+	if (!TransactionIdIsValid(nonremovable_xid))
+		return;
 
 	if (!TransactionIdIsValid(*xmin) ||
 		TransactionIdPrecedes(nonremovable_xid, *xmin))
@@ -1402,17 +1415,17 @@ acquire_conflict_slot_if_exists(void)
 }
 
 /*
- * Advance the xmin the replication slot used to retain information required
+ * Update the xmin the replication slot used to retain information required
  * for conflict detection.
  */
 static void
-advance_conflict_slot_xmin(TransactionId new_xmin)
+update_conflict_slot_xmin(TransactionId new_xmin)
 {
 	Assert(MyReplicationSlot);
-	Assert(TransactionIdIsValid(new_xmin));
-	Assert(TransactionIdPrecedesOrEquals(MyReplicationSlot->data.xmin, new_xmin));
+	Assert(!TransactionIdIsValid(new_xmin) ||
+		   TransactionIdPrecedesOrEquals(MyReplicationSlot->data.xmin, new_xmin));
 
-	/* Return if the xmin value of the slot cannot be advanced */
+	/* Return if the xmin value of the slot cannot be updated */
 	if (TransactionIdEquals(MyReplicationSlot->data.xmin, new_xmin))
 		return;
 
@@ -1518,7 +1531,7 @@ GetLeaderApplyWorkerPid(pid_t pid)
 Datum
 pg_stat_get_subscription(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_SUBSCRIPTION_COLS	10
+#define PG_STAT_GET_SUBSCRIPTION_COLS	11
 	Oid			subid = PG_ARGISNULL(0) ? InvalidOid : PG_GETARG_OID(0);
 	int			i;
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
@@ -1595,6 +1608,15 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
 				elog(ERROR, "unknown worker type");
 		}
 
+		/*
+		 * Only the leader apply worker manages conflict retention (see
+		 * maybe_advance_nonremovable_xid() for details).
+		 */
+		if (!isParallelApplyWorker(&worker) && !isTablesyncWorker(&worker))
+			values[10] = TransactionIdIsValid(worker.oldest_nonremovable_xid);
+		else
+			nulls[10] = true;
+
 		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
 							 values, nulls);
 
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 0fdc5de57ba..e327ffe8e00 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -415,6 +415,9 @@ typedef struct RetainDeadTuplesData
 										 * updated in final phase
 										 * (RDT_WAIT_FOR_LOCAL_FLUSH) */
 
+	long		table_sync_wait_time;	/* time spent waiting for table sync
+										 * to finish */
+
 	/*
 	 * The following fields are used to determine the timing for the next
 	 * round of transaction ID advancement.
@@ -555,6 +558,8 @@ static void request_publisher_status(RetainDeadTuplesData *rdt_data);
 static void wait_for_publisher_status(RetainDeadTuplesData *rdt_data,
 									  bool status_received);
 static void wait_for_local_flush(RetainDeadTuplesData *rdt_data);
+static void reset_retention_data_fields(RetainDeadTuplesData *rdt_data);
+static bool should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data);
 static void adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data,
 										bool new_xid_found);
 
@@ -3220,6 +3225,7 @@ FindDeletedTupleInLocalRel(Relation localrel, Oid localidxoid,
 {
 	TransactionId oldestxmin;
 	ReplicationSlot *slot;
+	bool		stop_retention;
 
 	/*
 	 * Return false if either dead tuples are not retained or commit timestamp
@@ -3228,6 +3234,42 @@ FindDeletedTupleInLocalRel(Relation localrel, Oid localidxoid,
 	if (!MySubscription->retaindeadtuples || !track_commit_timestamp)
 		return false;
 
+	/*
+	 * Check whether the leader apply worker has stopped retaining information
+	 * for detecting conflicts.
+	 */
+	if (am_leader_apply_worker())
+	{
+		stop_retention =
+			!TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid);
+	}
+	else
+	{
+		LogicalRepWorker *leader;
+
+		/*
+		 * Obtain the information from the leader apply worker as only the
+		 * leader manages conflict retention (see
+		 * maybe_advance_nonremovable_xid() for details).
+		 */
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		leader = logicalrep_worker_find(MyLogicalRepWorker->subid,
+										InvalidOid, false);
+
+		SpinLockAcquire(&leader->relmutex);
+		stop_retention = !TransactionIdIsValid(leader->oldest_nonremovable_xid);
+		SpinLockRelease(&leader->relmutex);
+		LWLockRelease(LogicalRepWorkerLock);
+	}
+
+	/*
+	 * Return false if the leader apply worker has stopped retaining
+	 * information for detecting conflicts. This implies that update_deleted
+	 * can no longer be reliably detected.
+	 */
+	if (stop_retention)
+		return false;
+
 	/*
 	 * For conflict detection, we use the conflict slot's xmin value instead
 	 * of invoking GetOldestNonRemovableTransactionId(). The slot.xmin acts as
@@ -3254,7 +3296,14 @@ FindDeletedTupleInLocalRel(Relation localrel, Oid localidxoid,
 	oldestxmin = slot->data.xmin;
 	SpinLockRelease(&slot->mutex);
 
-	Assert(TransactionIdIsValid(oldestxmin));
+	/*
+	 * Return if the conflict detection slot.xmin is set to
+	 * InvalidTransactionId. This occurs when the leader and all other apply
+	 * workers cease retention immediately after obtaining the
+	 * oldest_nonremovable_xid above.
+	 */
+	if (!TransactionIdIsValid(oldestxmin))
+		return false;
 
 	if (OidIsValid(localidxoid) &&
 		IsIndexUsableForFindingDeletedTuple(localidxoid, oldestxmin))
@@ -4110,7 +4159,8 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
 		 * Ensure to wake up when it's possible to advance the non-removable
 		 * transaction ID.
 		 */
-		if (rdt_data.phase == RDT_GET_CANDIDATE_XID &&
+		if (TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid) &&
+			rdt_data.phase == RDT_GET_CANDIDATE_XID &&
 			rdt_data.xid_advance_interval)
 			wait_time = Min(wait_time, rdt_data.xid_advance_interval);
 
@@ -4325,6 +4375,10 @@ can_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data)
 	if (!MySubscription->retaindeadtuples)
 		return false;
 
+	/* No need to advance if we have already stopped retaining */
+	if (!TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid))
+		return false;
+
 	return true;
 }
 
@@ -4468,6 +4522,13 @@ wait_for_publisher_status(RetainDeadTuplesData *rdt_data,
 	if (!status_received)
 		return;
 
+	/*
+	 * Stop retaining conflict information if required (See
+	 * should_stop_conflict_info_retention() for details).
+	 */
+	if (should_stop_conflict_info_retention(rdt_data))
+		return;
+
 	if (!FullTransactionIdIsValid(rdt_data->remote_wait_for))
 		rdt_data->remote_wait_for = rdt_data->remote_nextxid;
 
@@ -4549,6 +4610,27 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data)
 	 * have a WAL position greater than the rdt_data->remote_lsn.
 	 */
 	if (!AllTablesyncsReady())
+	{
+		TimestampTz now;
+
+		now = rdt_data->last_recv_time
+			? rdt_data->last_recv_time : GetCurrentTimestamp();
+
+		/*
+		 * Record the time spent waiting for table sync, it is needed for the
+		 * timeout check in should_stop_conflict_info_retention().
+		 */
+		rdt_data->table_sync_wait_time =
+			TimestampDifferenceMilliseconds(rdt_data->candidate_xid_time, now);
+
+		return;
+	}
+
+	/*
+	 * Stop retaining conflict information if required (See
+	 * should_stop_conflict_info_retention() for details).
+	 */
+	if (should_stop_conflict_info_retention(rdt_data))
 		return;
 
 	/*
@@ -4594,12 +4676,21 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data)
 	/* Notify launcher to update the xmin of the conflict slot */
 	ApplyLauncherWakeup();
 
-	/*
-	 * Reset all data fields except those used to determine the timing for the
-	 * next round of transaction ID advancement. We can even use
-	 * flushpos_update_time in the next round to decide whether to get the
-	 * latest flush position.
-	 */
+	reset_retention_data_fields(rdt_data);
+
+	/* process the next phase */
+	process_rdt_phase_transition(rdt_data, false);
+}
+
+/*
+ * Reset all data fields of RetainDeadTuplesData except those used to
+ * determine the timing for the next round of transaction ID advancement. We
+ * can even use flushpos_update_time in the next round to decide whether to get
+ * the latest flush position.
+ */
+static void
+reset_retention_data_fields(RetainDeadTuplesData *rdt_data)
+{
 	rdt_data->phase = RDT_GET_CANDIDATE_XID;
 	rdt_data->remote_lsn = InvalidXLogRecPtr;
 	rdt_data->remote_oldestxid = InvalidFullTransactionId;
@@ -4607,9 +4698,65 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data)
 	rdt_data->reply_time = 0;
 	rdt_data->remote_wait_for = InvalidFullTransactionId;
 	rdt_data->candidate_xid = InvalidTransactionId;
+	rdt_data->table_sync_wait_time = 0;
+}
 
-	/* process the next phase */
-	process_rdt_phase_transition(rdt_data, false);
+/*
+ * Check whether conflict information retention should be stopped because the
+ * wait time has exceeded the maximum limit (max_conflict_retention_duration).
+ *
+ * If retention should be stopped, set LogicalRepWorker->oldest_nonremovable_xid
+ * to InvalidTransactionId, notify the launcher to set the slot.xmin to
+ * InvalidTransactionId as well, and return true. Return false otherwise.
+ *
+ * Currently, the retention will not resume automatically unless user manually
+ * disables retain_dead_tuples and re-enables it after confirming that the
+ * replication slot has been dropped.
+ */
+static bool
+should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data)
+{
+	TimestampTz now;
+
+	Assert(TransactionIdIsValid(rdt_data->candidate_xid));
+	Assert(rdt_data->phase == RDT_WAIT_FOR_PUBLISHER_STATUS ||
+		   rdt_data->phase == RDT_WAIT_FOR_LOCAL_FLUSH);
+
+	if (!max_conflict_retention_duration)
+		return false;
+
+	/*
+	 * Use last_recv_time when applying changes in the loop to avoid
+	 * unnecessary system time retrieval. If last_recv_time is not available,
+	 * obtain the current timestamp.
+	 */
+	now = rdt_data->last_recv_time ? rdt_data->last_recv_time : GetCurrentTimestamp();
+
+	/*
+	 * Return if the wait time has not exceeded the maximum limit
+	 * (max_conflict_retention_duration).
+	 */
+	if (!TimestampDifferenceExceeds(rdt_data->candidate_xid_time, now,
+									max_conflict_retention_duration +
+									rdt_data->table_sync_wait_time))
+		return false;
+
+	ereport(LOG,
+			errmsg("logical replication worker for subscription \"%s\" will stop retaining conflict information",
+				   MySubscription->name),
+			errdetail("The time spent advancing the non-removable transaction ID has exceeded the maximum limit of %u ms.",
+					  max_conflict_retention_duration));
+
+	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
+	MyLogicalRepWorker->oldest_nonremovable_xid = InvalidTransactionId;
+	SpinLockRelease(&MyLogicalRepWorker->relmutex);
+
+	/* Notify launcher to update the conflict slot */
+	ApplyLauncherWakeup();
+
+	reset_retention_data_fields(rdt_data);
+
+	return true;
 }
 
 /*
@@ -4642,6 +4789,10 @@ adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found)
 		 */
 		rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval * 2,
 											 max_interval);
+
+		/* Ensure the wait time remains within the maximum limit */
+		rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval,
+											 max_conflict_retention_duration);
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index d14b1678e7f..580762c6a00 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3388,6 +3388,19 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"max_conflict_retention_duration",
+			PGC_SIGHUP,
+			REPLICATION_SUBSCRIBERS,
+			gettext_noop("Maximum duration for retaining information used in logical replication conflict detection."),
+			NULL,
+			GUC_UNIT_MS
+		},
+		&max_conflict_retention_duration,
+		0, 0, INT_MAX,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"log_rotation_age", PGC_SIGHUP, LOGGING_WHERE,
 			gettext_noop("Sets the amount of time to wait before forcing "
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index a9d8293474a..45c9e0a16a0 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -396,6 +396,7 @@
 					# (change requires restart)
 #max_sync_workers_per_subscription = 2	# taken from max_logical_replication_workers
 #max_parallel_apply_workers_per_subscription = 2	# taken from max_logical_replication_workers
+#max_conflict_retention_duration = 0	# in milliseconds; 0 disables
 
 
 #------------------------------------------------------------------------------
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 118d6da1ace..c284b4d2c6d 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5696,9 +5696,9 @@
   proname => 'pg_stat_get_subscription', prorows => '10', proisstrict => 'f',
   proretset => 't', provolatile => 's', proparallel => 'r',
   prorettype => 'record', proargtypes => 'oid',
-  proallargtypes => '{oid,oid,oid,int4,int4,pg_lsn,timestamptz,timestamptz,pg_lsn,timestamptz,text}',
-  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{subid,subid,relid,pid,leader_pid,received_lsn,last_msg_send_time,last_msg_receipt_time,latest_end_lsn,latest_end_time,worker_type}',
+  proallargtypes => '{oid,oid,oid,int4,int4,pg_lsn,timestamptz,timestamptz,pg_lsn,timestamptz,text,bool}',
+  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{subid,subid,relid,pid,leader_pid,received_lsn,last_msg_send_time,last_msg_receipt_time,latest_end_lsn,latest_end_time,worker_type,retain_dead_tuples}',
   prosrc => 'pg_stat_get_subscription' },
 { oid => '2026', descr => 'statistics: current backend PID',
   proname => 'pg_backend_pid', provolatile => 's', proparallel => 'r',
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index b29453e8e4f..6e3007db5f0 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -15,6 +15,7 @@
 extern PGDLLIMPORT int max_logical_replication_workers;
 extern PGDLLIMPORT int max_sync_workers_per_subscription;
 extern PGDLLIMPORT int max_parallel_apply_workers_per_subscription;
+extern PGDLLIMPORT int max_conflict_retention_duration;
 
 extern void ApplyLauncherRegister(void);
 extern void ApplyLauncherMain(Datum main_arg);
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 7c0204dd6f4..b86c759394f 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -94,6 +94,9 @@ typedef struct LogicalRepWorker
 	 * The logical replication launcher manages an internal replication slot
 	 * named "pg_conflict_detection". It asynchronously collects this ID to
 	 * decide when to advance the xmin value of the slot.
+	 *
+	 * This ID would be set to InvalidTransactionId if the apply worker has
+	 * stopped retaining information useful for conflict detection.
 	 */
 	TransactionId oldest_nonremovable_xid;
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 35e8aad7701..35c24285dd9 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2174,9 +2174,10 @@ pg_stat_subscription| SELECT su.oid AS subid,
     st.last_msg_send_time,
     st.last_msg_receipt_time,
     st.latest_end_lsn,
-    st.latest_end_time
+    st.latest_end_time,
+    st.retain_dead_tuples
    FROM (pg_subscription su
-     LEFT JOIN pg_stat_get_subscription(NULL::oid) st(subid, relid, pid, leader_pid, received_lsn, last_msg_send_time, last_msg_receipt_time, latest_end_lsn, latest_end_time, worker_type) ON ((st.subid = su.oid)));
+     LEFT JOIN pg_stat_get_subscription(NULL::oid) st(subid, relid, pid, leader_pid, received_lsn, last_msg_send_time, last_msg_receipt_time, latest_end_lsn, latest_end_time, worker_type, retain_dead_tuples) ON ((st.subid = su.oid)));
 pg_stat_subscription_stats| SELECT ss.subid,
     s.subname,
     ss.apply_error_count,
diff --git a/src/test/subscription/t/035_conflicts.pl b/src/test/subscription/t/035_conflicts.pl
index 36aeb14c563..aa6ef19dd70 100644
--- a/src/test/subscription/t/035_conflicts.pl
+++ b/src/test/subscription/t/035_conflicts.pl
@@ -214,6 +214,10 @@ ok( $node_B->poll_query_until(
 	),
 	"the xmin value of slot 'pg_conflict_detection' is valid on Node B");
 
+my $result = $node_B->safe_psql('postgres',
+	"SELECT retain_dead_tuples FROM pg_stat_subscription WHERE subname='$subname_BA';");
+is($result, qq(t), 'worker on node B retains conflict information');
+
 ##################################################
 # Check that the retain_dead_tuples option can be enabled only for disabled
 # subscriptions. Validate the NOTICE message during the subscription DDL, and
@@ -254,6 +258,10 @@ ok( $node_A->poll_query_until(
 	),
 	"the xmin value of slot 'pg_conflict_detection' is valid on Node A");
 
+$result = $node_A->safe_psql('postgres',
+	"SELECT retain_dead_tuples FROM pg_stat_subscription WHERE subname='$subname_AB';");
+is($result, qq(t), 'worker on node A retains conflict information');
+
 ##################################################
 # Check the WARNING when changing the origin to ANY, if retain_dead_tuples is
 # enabled. This warns of the possibility of receiving changes from origins
@@ -281,7 +289,7 @@ $node_A->psql('postgres',
 $node_A->safe_psql('postgres', "INSERT INTO tab VALUES (1, 1), (2, 2);");
 $node_A->wait_for_catchup($subname_BA);
 
-my $result = $node_B->safe_psql('postgres', "SELECT * FROM tab;");
+$result = $node_B->safe_psql('postgres', "SELECT * FROM tab;");
 is($result, qq(1|1
 2|2), 'check replicated insert on node B');
 
-- 
2.50.1.windows.1