v22-0002-Handle-logical-slot-conflicts-on-standby.patch

From c306b93841868c56ddc149ff089b13c7c6a8cf62 Mon Sep 17 00:00:00 2001
From: bdrouvotAWS <bdrouvot@amazon.com>
Date: Mon, 2 Aug 2021 13:55:45 +0000
Subject: [PATCH v22 2/5] Handle logical slot conflicts on standby.

During WAL replay on standby, when slot conflict is identified,
invalidate such slots. Also do the same thing if wal_level on master
is reduced to below logical and there are existing logical slots
on standby. Introduce a new ProcSignalReason value for slot
conflict recovery. Arrange for a new pg_stat_get_activity field:
confl_logicalslot.

Author: Andres Freund (in an older version), Amit Khandekar, Bertrand Drouvot
Reviewed-By: Bertrand Drouvot, Andres Freund, Robert Haas, Fabrizio de Royes Mello
---
 doc/src/sgml/monitoring.sgml                  |  10 +
 src/backend/access/gist/gistxlog.c            |   4 +-
 src/backend/access/hash/hash_xlog.c           |   3 +-
 src/backend/access/heap/heapam.c              |  10 +-
 src/backend/access/nbtree/nbtxlog.c           |   4 +-
 src/backend/access/spgist/spgxlog.c           |   1 +
 src/backend/access/transam/xlog.c             |  13 ++
 src/backend/catalog/system_views.sql          |   3 +-
 src/backend/postmaster/pgstat.c               |  20 ++
 .../replication/logical/logicalfuncs.c        |   7 +-
 src/backend/replication/slot.c                | 209 ++++++++++++++++++
 src/backend/replication/walsender.c           |   8 +
 src/backend/storage/ipc/procarray.c           |   4 +
 src/backend/storage/ipc/procsignal.c          |   3 +
 src/backend/storage/ipc/standby.c             |  11 +-
 src/backend/tcop/postgres.c                   |  22 ++
 src/backend/utils/adt/pgstatfuncs.c           |  16 ++
 src/include/catalog/pg_proc.dat               |   5 +
 src/include/pgstat.h                          |   2 +
 src/include/replication/slot.h                |   3 +
 src/include/storage/procsignal.h              |   1 +
 src/include/storage/standby.h                 |   4 +-
 src/test/regress/expected/rules.out           |   3 +-
 23 files changed, 351 insertions(+), 15 deletions(-)
   4.1% src/backend/access/heap/
   4.7% src/backend/access/transam/
   5.1% src/backend/access/
   4.3% src/backend/postmaster/
   3.5% src/backend/replication/logical/
  52.2% src/backend/replication/
   5.6% src/backend/storage/ipc/
   7.1% src/backend/tcop/
   3.6% src/backend/
   6.3% src/include/

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 74a58a916c..6072eee73e 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -4034,6 +4034,16 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
        deadlocks
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>confl_logicalslot</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of queries in this database that have been canceled due to
+       logical slots
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/access/gist/gistxlog.c b/src/backend/access/gist/gistxlog.c
index 46aee6f2a9..5963e639d8 100644
--- a/src/backend/access/gist/gistxlog.c
+++ b/src/backend/access/gist/gistxlog.c
@@ -195,7 +195,8 @@ gistRedoDeleteRecord(XLogReaderState *record)
 
 		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
 
-		ResolveRecoveryConflictWithSnapshot(xldata->latestRemovedXid, rnode);
+		ResolveRecoveryConflictWithSnapshot(xldata->latestRemovedXid,
+											xldata->onCatalogTable, rnode);
 	}
 
 	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
@@ -395,6 +396,7 @@ gistRedoPageReuse(XLogReaderState *record)
 	 */
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshotFullXid(xlrec->latestRemovedFullXid,
+												   xlrec->onCatalogTable,
 												   xlrec->node);
 }
 
diff --git a/src/backend/access/hash/hash_xlog.c b/src/backend/access/hash/hash_xlog.c
index 27475fcbd6..e5c6124400 100644
--- a/src/backend/access/hash/hash_xlog.c
+++ b/src/backend/access/hash/hash_xlog.c
@@ -1002,7 +1002,8 @@ hash_xlog_vacuum_one_page(XLogReaderState *record)
 		RelFileNode rnode;
 
 		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
-		ResolveRecoveryConflictWithSnapshot(xldata->latestRemovedXid, rnode);
+		ResolveRecoveryConflictWithSnapshot(xldata->latestRemovedXid,
+											xldata->onCatalogTable, rnode);
 	}
 
 	action = XLogReadBufferForRedoExtended(record, 0, RBM_NORMAL, true, &buffer);
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 4019a2122e..75ca5f79f4 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8419,7 +8419,8 @@ heap_xlog_prune(XLogReaderState *record)
 	 * no queries running for which the removed tuples are still visible.
 	 */
 	if (InHotStandby)
-		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid, rnode);
+		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
+											xlrec->onCatalogTable, rnode);
 
 	/*
 	 * If we have a full-page image, restore it (using a cleanup lock) and
@@ -8587,7 +8588,9 @@ heap_xlog_visible(XLogReaderState *record)
 	 * rather than killing the transaction outright.
 	 */
 	if (InHotStandby)
-		ResolveRecoveryConflictWithSnapshot(xlrec->cutoff_xid, rnode);
+		ResolveRecoveryConflictWithSnapshot(xlrec->cutoff_xid,
+											xlrec->onCatalogTable,
+											rnode);
 
 	/*
 	 * Read the heap page, if it still exists. If the heap file has dropped or
@@ -8724,7 +8727,8 @@ heap_xlog_freeze_page(XLogReaderState *record)
 		TransactionIdRetreat(latestRemovedXid);
 
 		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
-		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid,
+											xlrec->onCatalogTable, rnode);
 	}
 
 	if (XLogReadBufferForRedo(record, 0, &buffer) == BLK_NEEDS_REDO)
diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 786c08c0ce..41b7ec8e2d 100644
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -668,7 +668,8 @@ btree_xlog_delete(XLogReaderState *record)
 
 		XLogRecGetBlockTag(record, 0, &rnode, NULL, NULL);
 
-		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid, rnode);
+		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
+											xlrec->onCatalogTable, rnode);
 	}
 
 	/*
@@ -1006,6 +1007,7 @@ btree_xlog_reuse_page(XLogReaderState *record)
 
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshotFullXid(xlrec->latestRemovedFullXid,
+												   xlrec->onCatalogTable,
 												   xlrec->node);
 }
 
diff --git a/src/backend/access/spgist/spgxlog.c b/src/backend/access/spgist/spgxlog.c
index 3dfd2aa317..add4da4e74 100644
--- a/src/backend/access/spgist/spgxlog.c
+++ b/src/backend/access/spgist/spgxlog.c
@@ -881,6 +881,7 @@ spgRedoVacuumRedirect(XLogReaderState *record)
 
 			XLogRecGetBlockTag(record, 0, &node, NULL, NULL);
 			ResolveRecoveryConflictWithSnapshot(xldata->newestRedirectXid,
+												xldata->onCatalogTable,
 												node);
 		}
 	}
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f84c0bb01e..1ff7751857 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -10397,6 +10397,19 @@ xlog_redo(XLogReaderState *record)
 		/* Update our copy of the parameters in pg_control */
 		memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_parameter_change));
 
+		/*
+		 * Invalidate logical slots if we are in hot standby and the primary does not
+		 * have a WAL level sufficient for logical decoding. No need to search
+		 * for potentially conflicting logically slots if standby is running
+		 * with wal_level lower than logical, because in that case, we would
+		 * have either disallowed creation of logical slots or invalidated existing
+		 * ones.
+		 */
+		if (InRecovery && InHotStandby &&
+			xlrec.wal_level < WAL_LEVEL_LOGICAL &&
+			wal_level >= WAL_LEVEL_LOGICAL)
+			InvalidateConflictingLogicalReplicationSlots(InvalidOid,InvalidTransactionId);
+
 		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
 		ControlFile->MaxConnections = xlrec.MaxConnections;
 		ControlFile->max_worker_processes = xlrec.max_worker_processes;
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 55f6e3711d..cd1fc88d17 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1020,7 +1020,8 @@ CREATE VIEW pg_stat_database_conflicts AS
             pg_stat_get_db_conflict_lock(D.oid) AS confl_lock,
             pg_stat_get_db_conflict_snapshot(D.oid) AS confl_snapshot,
             pg_stat_get_db_conflict_bufferpin(D.oid) AS confl_bufferpin,
-            pg_stat_get_db_conflict_startup_deadlock(D.oid) AS confl_deadlock
+            pg_stat_get_db_conflict_startup_deadlock(D.oid) AS confl_deadlock,
+            pg_stat_get_db_conflict_logicalslot(D.oid) AS confl_logicalslot
     FROM pg_database D;
 
 CREATE VIEW pg_stat_user_functions AS
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 11702f2a80..556a515608 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1863,6 +1863,22 @@ pgstat_report_replslot_drop(const char *slotname)
 	pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
 }
 
+/* ----------
+ * pgstat_report_replslot_conflict()
+ * Tell the collector about a logical slot being conflicting
+ * with recovery.
+ * ----------
+ */
+void
+pgstat_report_replslot_conflict(Oid dboid)
+{
+	PgStat_MsgRecoveryConflict msg;
+	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RECOVERYCONFLICT);
+	msg.m_databaseid = dboid;
+	msg.m_reason = PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT;
+	pgstat_send(&msg, sizeof(msg));
+}
+
 /* ----------
  * pgstat_ping() -
  *
@@ -3489,6 +3505,7 @@ reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
 	dbentry->n_conflict_tablespace = 0;
 	dbentry->n_conflict_lock = 0;
 	dbentry->n_conflict_snapshot = 0;
+	dbentry->n_conflict_logicalslot = 0;
 	dbentry->n_conflict_bufferpin = 0;
 	dbentry->n_conflict_startup_deadlock = 0;
 	dbentry->n_temp_files = 0;
@@ -5425,6 +5442,9 @@ pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len)
 		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
 			dbentry->n_conflict_snapshot++;
 			break;
+		case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+			dbentry->n_conflict_logicalslot++;
+			break;
 		case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
 			dbentry->n_conflict_bufferpin++;
 			break;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 1f38c5b33e..1d9400ea63 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -241,11 +241,14 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 		/*
 		 * After the sanity checks in CreateDecodingContext, make sure the
-		 * restart_lsn is valid.  Avoid "cannot get changes" wording in this
+		 * restart_lsn is valid or both xmin and catalog_xmin are valid.
+		 * Avoid "cannot get changes" wording in this
 		 * errmsg because that'd be confusingly ambiguous about no changes
 		 * being available.
 		 */
-		if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
+		if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn)
+			|| (!TransactionIdIsValid(MyReplicationSlot->data.xmin)
+				&& !TransactionIdIsValid(MyReplicationSlot->data.catalog_xmin)))
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 					 errmsg("can no longer get changes from replication slot \"%s\"",
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 33e9acab4a..6e89bab255 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1338,6 +1338,215 @@ restart:
 	return invalidated;
 }
 
+/*
+ * Helper for InvalidateConflictingLogicalReplicationSlot -- acquires the given slot
+ * and mark it invalid, if necessary and possible.
+ *
+ * Returns whether ReplicationSlotControlLock was released in the interim (and
+ * in that case we're not holding the lock at return, otherwise we are).
+ *
+ * This is inherently racy, because we release the LWLock
+ * for syscalls, so caller must restart if we return true.
+ */
+static bool
+InvalidatePossiblyConflictingLogicalReplicationSlot(ReplicationSlot *s, TransactionId xid)
+{
+	int		last_signaled_pid = 0;
+	bool	released_lock = false;
+
+	for (;;)
+	{
+		TransactionId slot_xmin;
+		TransactionId slot_catalog_xmin;
+		NameData	slotname;
+		int			active_pid = 0;
+
+		Assert(LWLockHeldByMeInMode(ReplicationSlotControlLock, LW_SHARED));
+
+		if (!s->in_use)
+		{
+			if (released_lock)
+				LWLockRelease(ReplicationSlotControlLock);
+			break;
+		}
+
+		/*
+		 * Check if the slot needs to be invalidated. If it needs to be
+		 * invalidated, and is not currently acquired, acquire it and mark it
+		 * as having been invalidated. We do this with the spinlock held to
+		 * avoid race conditions -- for example the xmin(s) could move forward
+		 * , or the slot could be dropped.
+		 */
+		SpinLockAcquire(&s->mutex);
+
+		slot_xmin = s->data.xmin;
+		slot_catalog_xmin = s->data.catalog_xmin;
+
+		/*
+		 * If the slot is already invalid or is not conflicting, we don't need to
+		 * do anything.
+		 */
+
+		/* slot has been invalidated */
+		if ((!TransactionIdIsValid(slot_xmin) && !TransactionIdIsValid(slot_catalog_xmin))
+			||
+		/*
+		 * we are not forcing for invalidation because the xid is valid
+		 * and this is a non conflicting slot
+		 */
+			(TransactionIdIsValid(xid) && !(
+				(TransactionIdIsValid(slot_xmin) && TransactionIdPrecedesOrEquals(slot_xmin, xid))
+				||
+				(TransactionIdIsValid(slot_catalog_xmin) && TransactionIdPrecedesOrEquals(slot_catalog_xmin, xid))
+				))
+			)
+		{
+			SpinLockRelease(&s->mutex);
+			if (released_lock)
+				LWLockRelease(ReplicationSlotControlLock);
+			break;
+		}
+
+		slotname = s->data.name;
+		active_pid = s->active_pid;
+
+		/*
+		 * If the slot can be acquired, do so and mark it invalidated
+		 * immediately.  Otherwise we'll signal the owning process, below, and
+		 * retry.
+		 */
+		if (active_pid == 0)
+		{
+			MyReplicationSlot = s;
+			s->active_pid = MyProcPid;
+			s->data.xmin = InvalidTransactionId;
+			s->data.catalog_xmin = InvalidTransactionId;
+		}
+
+		SpinLockRelease(&s->mutex);
+
+		if (active_pid != 0)
+		{
+			/*
+			 * Prepare the sleep on the slot's condition variable before
+			 * releasing the lock, to close a possible race condition if the
+			 * slot is released before the sleep below.
+			 */
+
+			ConditionVariablePrepareToSleep(&s->active_cv);
+
+			LWLockRelease(ReplicationSlotControlLock);
+			released_lock = true;
+
+			/*
+			 * Signal to terminate the process that owns the slot, if we
+			 * haven't already signalled it.  (Avoidance of repeated
+			 * signalling is the only reason for there to be a loop in this
+			 * routine; otherwise we could rely on caller's restart loop.)
+			 *
+			 * There is the race condition that other process may own the slot
+			 * after its current owner process is terminated and before this
+			 * process owns it. To handle that, we signal only if the PID of
+			 * the owning process has changed from the previous time. (This
+			 * logic assumes that the same PID is not reused very quickly.)
+			 */
+			if (last_signaled_pid != active_pid)
+			{
+				ereport(LOG,
+						(errmsg("terminating process %d because replication slot \"%s\" conflicts with recovery",
+								active_pid, NameStr(slotname))));
+
+				(void) kill(active_pid, SIGTERM);
+				last_signaled_pid = active_pid;
+			}
+
+			/* Wait until the slot is released. */
+			ConditionVariableSleep(&s->active_cv,
+									WAIT_EVENT_REPLICATION_SLOT_DROP);
+
+			/*
+			 * Re-acquire lock and start over; we expect to invalidate the
+			 * slot next time (unless another process acquires the slot in the
+			 * meantime).
+			 */
+			LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+			continue;
+		}
+		else
+		{
+			/*
+			 * We hold the slot now and have already invalidated it; flush it
+			 * to ensure that state persists.
+			 *
+			 * Don't want to hold ReplicationSlotControlLock across file
+			 * system operations, so release it now but be sure to tell caller
+			 * to restart from scratch.
+			 */
+			LWLockRelease(ReplicationSlotControlLock);
+			released_lock = true;
+
+			/* Make sure the invalidated state persists across server restart */
+			ReplicationSlotMarkDirty();
+			ReplicationSlotSave();
+			ReplicationSlotRelease();
+			pgstat_report_replslot_conflict(s->data.database);
+
+			ereport(LOG,
+					(errmsg("invalidating slot \"%s\" because it conflicts with recovery", NameStr(slotname))));
+
+			/* done with this slot for now */
+			break;
+		}
+	}
+
+	Assert(!released_lock == LWLockHeldByMeInMode(ReplicationSlotControlLock, LW_SHARED));
+
+	return released_lock;
+}
+
+/*
+ * Resolve recovery conflicts with logical slots.
+ *
+ * When xid is valid, it means that we are about to remove rows older than xid.
+ * Therefore we need to invalidate slots that depend on seeing those rows.
+ * When xid is invalid, invalidate all logical slots. This is required when the
+ * master wal_level is set back to replica, so existing logical slots need to
+ * be invalidated.
+ */
+void
+InvalidateConflictingLogicalReplicationSlots(Oid dboid, TransactionId xid)
+{
+
+	Assert(max_replication_slots >= 0);
+
+	if (max_replication_slots == 0)
+		return;
+restart:
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+	for (int i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
+
+		if (!s->in_use)
+			continue;
+
+		/* We are only dealing with *logical* slot conflicts. */
+		if (!SlotIsLogical(s))
+			continue;
+
+		/* not our database and we don't want all the database, skip */
+		if (s->data.database != dboid && TransactionIdIsValid(xid))
+			continue;
+
+		if (InvalidatePossiblyConflictingLogicalReplicationSlot(s, xid))
+		{
+			/* if the lock was released, we need to restart from scratch */
+			goto restart;
+		}
+	}
+	LWLockRelease(ReplicationSlotControlLock);
+}
+
 /*
  * Flush all replication slots to disk.
  *
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 3ca2a11389..d0e247b104 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1147,6 +1147,14 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 
 	ReplicationSlotAcquire(cmd->slotname, true);
 
+	if (!TransactionIdIsValid(MyReplicationSlot->data.xmin)
+		 && !TransactionIdIsValid(MyReplicationSlot->data.catalog_xmin))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot read from logical replication slot \"%s\"",
+						cmd->slotname),
+				 errdetail("This slot has been invalidated because it was conflicting with recovery.")));
+
 	if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index c7816fcfb3..0c555a390c 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3443,6 +3443,10 @@ SignalVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode,
 
 		GET_VXID_FROM_PGPROC(procvxid, *proc);
 
+		/*
+		 * Note: vxid.localTransactionId can be invalid, which means the
+		 * request is to signal the pid that is not running a transaction.
+		 */
 		if (procvxid.backendId == vxid.backendId &&
 			procvxid.localTransactionId == vxid.localTransactionId)
 		{
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index defb75aa26..315d5a1e33 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -673,6 +673,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT))
+		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT);
+
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 077251c1a6..28121f0658 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -34,6 +34,7 @@
 #include "utils/ps_status.h"
 #include "utils/timeout.h"
 #include "utils/timestamp.h"
+#include "replication/slot.h"
 
 /* User-settable GUC parameters */
 int			vacuum_defer_cleanup_age;
@@ -440,7 +441,8 @@ ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
 }
 
 void
-ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode node)
+ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
+									bool onCatalogTable, RelFileNode node)
 {
 	VirtualTransactionId *backends;
 
@@ -465,6 +467,9 @@ ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode
 										   PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
 										   WAIT_EVENT_RECOVERY_CONFLICT_SNAPSHOT,
 										   true);
+
+	if (onCatalogTable)
+		InvalidateConflictingLogicalReplicationSlots(node.dbNode, latestRemovedXid);
 }
 
 /*
@@ -473,7 +478,7 @@ ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode
  */
 void
 ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId latestRemovedFullXid,
-										   RelFileNode node)
+										   bool onCatalogTable, RelFileNode node)
 {
 	/*
 	 * ResolveRecoveryConflictWithSnapshot operates on 32-bit TransactionIds,
@@ -491,7 +496,7 @@ ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId latestRemovedFullXi
 		TransactionId latestRemovedXid;
 
 		latestRemovedXid = XidFromFullTransactionId(latestRemovedFullXid);
-		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, node);
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, onCatalogTable, node);
 	}
 }
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 530caa520b..fc003299dc 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2467,6 +2467,9 @@ errdetail_recovery_conflict(void)
 		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
 			errdetail("User query might have needed to see row versions that must be removed.");
 			break;
+		case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+			errdetail("User was using the logical slot that must be dropped.");
+			break;
 		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
 			errdetail("User transaction caused buffer deadlock with recovery.");
 			break;
@@ -3037,6 +3040,25 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 			case PROCSIG_RECOVERY_CONFLICT_LOCK:
 			case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
 			case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
+			case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+				/*
+				 * For conflicts that require a logical slot to be invalidated, the
+				 * requirement is for the signal receiver to release the slot,
+				 * so that it could be invalidated by the signal sender. So for
+				 * normal backends, the transaction should be aborted, just
+				 * like for other recovery conflicts. But if it's walsender on
+				 * standby, then it has to be killed so as to release an
+				 * acquired logical slot.
+				 */
+				if (am_cascading_walsender &&
+					reason == PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT &&
+					MyReplicationSlot && SlotIsLogical(MyReplicationSlot))
+				{
+					RecoveryConflictPending = true;
+					QueryCancelPending = true;
+					InterruptPending = true;
+					break;
+				}
 
 				/*
 				 * If we aren't in a transaction any longer then ignore.
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index f0e09eae4d..5db0a29740 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1500,6 +1500,21 @@ pg_stat_get_db_conflict_snapshot(PG_FUNCTION_ARGS)
 	PG_RETURN_INT64(result);
 }
 
+Datum
+pg_stat_get_db_conflict_logicalslot(PG_FUNCTION_ARGS)
+{
+	Oid			dbid = PG_GETARG_OID(0);
+	int64		result;
+	PgStat_StatDBEntry *dbentry;
+
+	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
+		result = 0;
+	else
+		result = (int64) (dbentry->n_conflict_logicalslot);
+
+	PG_RETURN_INT64(result);
+}
+
 Datum
 pg_stat_get_db_conflict_bufferpin(PG_FUNCTION_ARGS)
 {
@@ -1543,6 +1558,7 @@ pg_stat_get_db_conflict_all(PG_FUNCTION_ARGS)
 		result = (int64) (dbentry->n_conflict_tablespace +
 						  dbentry->n_conflict_lock +
 						  dbentry->n_conflict_snapshot +
+						  dbentry->n_conflict_logicalslot +
 						  dbentry->n_conflict_bufferpin +
 						  dbentry->n_conflict_startup_deadlock);
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 8cd0252082..6dfcfa983f 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5438,6 +5438,11 @@
   proname => 'pg_stat_get_db_conflict_snapshot', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_conflict_snapshot' },
+{ oid => '4544',
+  descr => 'statistics: recovery conflicts in database caused by logical replication slot',
+  proname => 'pg_stat_get_db_conflict_logicalslot', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_conflict_logicalslot' },
 { oid => '3068',
   descr => 'statistics: recovery conflicts in database caused by shared buffer pin',
   proname => 'pg_stat_get_db_conflict_bufferpin', provolatile => 's',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 9612c0a6c2..52623b4be9 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -743,6 +743,7 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter n_conflict_tablespace;
 	PgStat_Counter n_conflict_lock;
 	PgStat_Counter n_conflict_snapshot;
+	PgStat_Counter n_conflict_logicalslot;
 	PgStat_Counter n_conflict_bufferpin;
 	PgStat_Counter n_conflict_startup_deadlock;
 	PgStat_Counter n_temp_files;
@@ -1011,6 +1012,7 @@ extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_replslot(const PgStat_StatReplSlotEntry *repSlotStat);
 extern void pgstat_report_replslot_create(const char *slotname);
 extern void pgstat_report_replslot_drop(const char *slotname);
+extern void pgstat_report_replslot_conflict(Oid dbOid);
 
 extern void pgstat_initialize(void);
 
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index e32fb85db8..4779617cd7 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -214,6 +214,7 @@ extern XLogRecPtr ReplicationSlotsComputeLogicalRestartLSN(void);
 extern bool ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive);
 extern void ReplicationSlotsDropDBSlots(Oid dboid);
 extern bool InvalidateObsoleteReplicationSlots(XLogSegNo oldestSegno);
+extern void InvalidateConflictingLogicalReplicationSlots(Oid dboid, TransactionId xid);
 extern ReplicationSlot *SearchNamedReplicationSlot(const char *name, bool need_lock);
 extern void ReplicationSlotNameForTablesync(Oid suboid, Oid relid, char *syncslotname, int szslot);
 extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok);
@@ -223,4 +224,6 @@ extern void CheckPointReplicationSlots(void);
 
 extern void CheckSlotRequirements(void);
 
+extern void ResolveRecoveryConflictWithLogicalSlots(Oid dboid, TransactionId xid, char *reason);
+
 #endif							/* SLOT_H */
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index eec186be2e..f86b070dbc 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -41,6 +41,7 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_TABLESPACE,
 	PROCSIG_RECOVERY_CONFLICT_LOCK,
 	PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
+	PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT,
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 38fd85a431..3ba1882216 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -30,9 +30,9 @@ extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
-												RelFileNode node);
+												bool onCatalogTable, RelFileNode node);
 extern void ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId latestRemovedFullXid,
-													   RelFileNode node);
+													   bool onCatalogTable, RelFileNode node);
 extern void ResolveRecoveryConflictWithTablespace(Oid tsid);
 extern void ResolveRecoveryConflictWithDatabase(Oid dbid);
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index e5ab11275d..66f28b649d 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1871,7 +1871,8 @@ pg_stat_database_conflicts| SELECT d.oid AS datid,
     pg_stat_get_db_conflict_lock(d.oid) AS confl_lock,
     pg_stat_get_db_conflict_snapshot(d.oid) AS confl_snapshot,
     pg_stat_get_db_conflict_bufferpin(d.oid) AS confl_bufferpin,
-    pg_stat_get_db_conflict_startup_deadlock(d.oid) AS confl_deadlock
+    pg_stat_get_db_conflict_startup_deadlock(d.oid) AS confl_deadlock,
+    pg_stat_get_db_conflict_logicalslot(d.oid) AS confl_logicalslot
    FROM pg_database d;
 pg_stat_gssapi| SELECT s.pid,
     s.gss_auth AS gss_authenticated,
-- 
2.18.4