Handle logical slot conflicts on standby

During WAL replay on the standby, when a conflict with a logical slot is
identified, invalidate such slots. There are two sources of conflicts:
1) Using the information added in 6af1793, logical slots are invalidated if
   required rows are removed
2) wal_level on the primary server is reduced to below logical

Uses the infrastructure introduced in the prior commit. FIXME: add commit
reference.

Change InvalidatePossiblyObsoleteSlot() to use a recovery conflict to
interrupt use of a slot, if called in the startup process. The new recovery
conflict is added to pg_stat_database_conflicts, as confl_active_logicalslot.

See 6af1793 for an overall design of logical decoding on a standby.

Bumps catversion for the addition of the pg_stat_database_conflicts column.
Bumps PGSTAT_FILE_FORMAT_ID for the same reason.

Author: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Amit Khandekar <amitdkhan.pg@gmail.com> (in an older version)
Reviewed-by: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20230407075009.igg7be27ha2htkbt@awork3.anarazel.de

Author: anarazel

doc/src/sgml/monitoring.sgml

@@ -4742,6 +4742,17 @@ 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_active_logicalslot</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of uses of logical slots in this database that have been
+       canceled due to old snapshots or a too low <xref linkend="guc-wal-level"/>
+       on the primary
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>

src/backend/access/gist/gistxlog.c

@@ -197,6 +197,7 @@ gistRedoDeleteRecord(XLogReaderState *record)
 		XLogRecGetBlockTag(record, 0, &rlocator, NULL, NULL);
 
 		ResolveRecoveryConflictWithSnapshot(xldata->snapshotConflictHorizon,
+											xldata->isCatalogRel,
 											rlocator);
 	}
 
@@ -390,6 +391,7 @@ gistRedoPageReuse(XLogReaderState *record)
 	 */
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshotFullXid(xlrec->snapshotConflictHorizon,
+												   xlrec->isCatalogRel,
 												   xlrec->locator);
 }
 

src/backend/access/hash/hash_xlog.c

@@ -1003,6 +1003,7 @@ hash_xlog_vacuum_one_page(XLogReaderState *record)
 
 		XLogRecGetBlockTag(record, 0, &rlocator, NULL, NULL);
 		ResolveRecoveryConflictWithSnapshot(xldata->snapshotConflictHorizon,
+											xldata->isCatalogRel,
 											rlocator);
 	}
 

src/backend/access/heap/heapam.c

@@ -8769,6 +8769,7 @@ heap_xlog_prune(XLogReaderState *record)
 	 */
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshot(xlrec->snapshotConflictHorizon,
+											xlrec->isCatalogRel,
 											rlocator);
 
 	/*
@@ -8940,6 +8941,7 @@ heap_xlog_visible(XLogReaderState *record)
 	 */
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshot(xlrec->snapshotConflictHorizon,
+											xlrec->flags & VISIBILITYMAP_XLOG_CATALOG_REL,
 											rlocator);
 
 	/*
@@ -9061,6 +9063,7 @@ heap_xlog_freeze_page(XLogReaderState *record)
 
 		XLogRecGetBlockTag(record, 0, &rlocator, NULL, NULL);
 		ResolveRecoveryConflictWithSnapshot(xlrec->snapshotConflictHorizon,
+											xlrec->isCatalogRel,
 											rlocator);
 	}
 

src/backend/access/nbtree/nbtxlog.c

@@ -669,6 +669,7 @@ btree_xlog_delete(XLogReaderState *record)
 		XLogRecGetBlockTag(record, 0, &rlocator, NULL, NULL);
 
 		ResolveRecoveryConflictWithSnapshot(xlrec->snapshotConflictHorizon,
+											xlrec->isCatalogRel,
 											rlocator);
 	}
 
@@ -1007,6 +1008,7 @@ btree_xlog_reuse_page(XLogReaderState *record)
 
 	if (InHotStandby)
 		ResolveRecoveryConflictWithSnapshotFullXid(xlrec->snapshotConflictHorizon,
+												   xlrec->isCatalogRel,
 												   xlrec->locator);
 }
 

src/backend/access/spgist/spgxlog.c

@@ -879,6 +879,7 @@ spgRedoVacuumRedirect(XLogReaderState *record)
 
 		XLogRecGetBlockTag(record, 0, &locator, NULL, NULL);
 		ResolveRecoveryConflictWithSnapshot(xldata->snapshotConflictHorizon,
+											xldata->isCatalogRel,
 											locator);
 	}
 

src/backend/access/transam/xlog.c

@@ -7970,6 +7970,21 @@ 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)
+			InvalidateObsoleteReplicationSlots(RS_INVAL_WAL_LEVEL,
+											   0, InvalidOid,
+											   InvalidTransactionId);
+
 		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
 		ControlFile->MaxConnections = xlrec.MaxConnections;
 		ControlFile->max_worker_processes = xlrec.max_worker_processes;

src/backend/catalog/system_views.sql

@@ -1069,7 +1069,8 @@ 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_active_logicalslot
     FROM pg_database D;
 
 CREATE VIEW pg_stat_user_functions AS

src/backend/replication/slot.c

@@ -1442,7 +1442,13 @@ InvalidatePossiblyObsoleteSlot(ReplicationSlotInvalidationCause cause,
 									   slotname, restart_lsn,
 									   oldestLSN, snapshotConflictHorizon);
 
-				(void) kill(active_pid, SIGTERM);
+				if (MyBackendType == B_STARTUP)
+					(void) SendProcSignal(active_pid,
+										  PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT,
+										  InvalidBackendId);
+				else
+					(void) kill(active_pid, SIGTERM);
+
 				last_signaled_pid = active_pid;
 			}
 

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);
 

src/backend/storage/ipc/standby.c

@@ -24,6 +24,7 @@
 #include "access/xlogutils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "replication/slot.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "storage/proc.h"
@@ -466,6 +467,7 @@ ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
  */
 void
 ResolveRecoveryConflictWithSnapshot(TransactionId snapshotConflictHorizon,
+									bool isCatalogRel,
 									RelFileLocator locator)
 {
 	VirtualTransactionId *backends;
@@ -491,6 +493,16 @@ ResolveRecoveryConflictWithSnapshot(TransactionId snapshotConflictHorizon,
 										   PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
 										   WAIT_EVENT_RECOVERY_CONFLICT_SNAPSHOT,
 										   true);
+
+	/*
+	 * Note that WaitExceedsMaxStandbyDelay() is not taken into account here
+	 * (as opposed to ResolveRecoveryConflictWithVirtualXIDs() above). That
+	 * seems OK, given that this kind of conflict should not normally be
+	 * reached, e.g. due to using a physical replication slot.
+	 */
+	if (wal_level >= WAL_LEVEL_LOGICAL && isCatalogRel)
+		InvalidateObsoleteReplicationSlots(RS_INVAL_HORIZON, 0, locator.dbOid,
+										   snapshotConflictHorizon);
 }
 
 /*
@@ -499,6 +511,7 @@ ResolveRecoveryConflictWithSnapshot(TransactionId snapshotConflictHorizon,
  */
 void
 ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId snapshotConflictHorizon,
+										   bool isCatalogRel,
 										   RelFileLocator locator)
 {
 	/*
@@ -517,7 +530,9 @@ ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId snapshotConflictHor
 		TransactionId truncated;
 
 		truncated = XidFromFullTransactionId(snapshotConflictHorizon);
-		ResolveRecoveryConflictWithSnapshot(truncated, locator);
+		ResolveRecoveryConflictWithSnapshot(truncated,
+											isCatalogRel,
+											locator);
 	}
 }
 
@@ -1478,6 +1493,9 @@ get_recovery_conflict_desc(ProcSignalReason reason)
 		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
 			reasonDesc = _("recovery conflict on snapshot");
 			break;
+		case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+			reasonDesc = _("recovery conflict on replication slot");
+			break;
 		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
 			reasonDesc = _("recovery conflict on buffer deadlock");
 			break;

src/backend/tcop/postgres.c

@@ -2526,6 +2526,9 @@ 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 a logical slot that must be invalidated.");
+			break;
 		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
 			errdetail("User transaction caused buffer deadlock with recovery.");
 			break;
@@ -3143,6 +3146,12 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 				InterruptPending = true;
 				break;
 
+			case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+				RecoveryConflictPending = true;
+				QueryCancelPending = true;
+				InterruptPending = true;
+				break;
+
 			default:
 				elog(FATAL, "unrecognized conflict mode: %d",
 					 (int) reason);

src/backend/utils/activity/pgstat_database.c

@@ -109,6 +109,9 @@ pgstat_report_recovery_conflict(int reason)
 		case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
 			dbentry->conflict_bufferpin++;
 			break;
+		case PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT:
+			dbentry->conflict_logicalslot++;
+			break;
 		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
 			dbentry->conflict_startup_deadlock++;
 			break;
@@ -387,6 +390,7 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(conflict_tablespace);
 	PGSTAT_ACCUM_DBCOUNT(conflict_lock);
 	PGSTAT_ACCUM_DBCOUNT(conflict_snapshot);
+	PGSTAT_ACCUM_DBCOUNT(conflict_logicalslot);
 	PGSTAT_ACCUM_DBCOUNT(conflict_bufferpin);
 	PGSTAT_ACCUM_DBCOUNT(conflict_startup_deadlock);
 

src/backend/utils/adt/pgstatfuncs.c

@@ -1071,6 +1071,8 @@ PG_STAT_GET_DBENTRY_INT64(xact_commit)
 /* pg_stat_get_db_xact_rollback */
 PG_STAT_GET_DBENTRY_INT64(xact_rollback)
 
+/* pg_stat_get_db_conflict_logicalslot */
+PG_STAT_GET_DBENTRY_INT64(conflict_logicalslot)
 
 Datum
 pg_stat_get_db_stat_reset_time(PG_FUNCTION_ARGS)
@@ -1104,6 +1106,7 @@ pg_stat_get_db_conflict_all(PG_FUNCTION_ARGS)
 		result = (int64) (dbentry->conflict_tablespace +
 						  dbentry->conflict_lock +
 						  dbentry->conflict_snapshot +
+						  dbentry->conflict_logicalslot +
 						  dbentry->conflict_bufferpin +
 						  dbentry->conflict_startup_deadlock);
 

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202304073
+#define CATALOG_VERSION_NO	202304074
 
 #endif

src/include/catalog/pg_proc.dat

@@ -5611,6 +5611,11 @@
   proname => 'pg_stat_get_db_conflict_snapshot', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_conflict_snapshot' },
+{ oid => '9901',
+  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',

src/include/pgstat.h

@@ -235,7 +235,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCAB
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCAC
 
 typedef struct PgStat_ArchiverStats
 {
@@ -332,6 +332,7 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter conflict_tablespace;
 	PgStat_Counter conflict_lock;
 	PgStat_Counter conflict_snapshot;
+	PgStat_Counter conflict_logicalslot;
 	PgStat_Counter conflict_bufferpin;
 	PgStat_Counter conflict_startup_deadlock;
 	PgStat_Counter temp_files;

src/include/storage/procsignal.h

@@ -42,6 +42,7 @@ 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,
 

src/include/storage/standby.h

@@ -30,8 +30,10 @@ extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId snapshotConflictHorizon,
+												bool isCatalogRel,
 												RelFileLocator locator);
 extern void ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId snapshotConflictHorizon,
+													   bool isCatalogRel,
 													   RelFileLocator locator);
 extern void ResolveRecoveryConflictWithTablespace(Oid tsid);
 extern void ResolveRecoveryConflictWithDatabase(Oid dbid);

src/test/regress/expected/rules.out

@@ -1870,7 +1870,8 @@ pg_stat_database_conflicts| SELECT oid AS datid,
     pg_stat_get_db_conflict_lock(oid) AS confl_lock,
     pg_stat_get_db_conflict_snapshot(oid) AS confl_snapshot,
     pg_stat_get_db_conflict_bufferpin(oid) AS confl_bufferpin,
-    pg_stat_get_db_conflict_startup_deadlock(oid) AS confl_deadlock
+    pg_stat_get_db_conflict_startup_deadlock(oid) AS confl_deadlock,
+    pg_stat_get_db_conflict_logicalslot(oid) AS confl_active_logicalslot
    FROM pg_database d;
 pg_stat_gssapi| SELECT pid,
     gss_auth AS gss_authenticated,