Add injection points to test replication slot advance

New injection points:

* checkpoint-before-old-wal-removal - triggered in the checkpointer
  process just before old WAL segments cleanup.

* logical-replication-slot-advance-segment - triggered in
  LogicalConfirmReceivedLocation when restart_lsn was changed enough to
  point to a next WAL segment.

Original patch by: Tomas Vondra <[email protected]>
Modified by: Vitaly Davydov <[email protected]>
Discussion: https://www.postgresql.org/message-id/flat/1d12d2-67235980-35-19a406a0%4063439497

Author: tvondra

src/backend/access/transam/xlog.c

@@ -7498,6 +7498,10 @@ CreateCheckPoint(int flags)
 	if (PriorRedoPtr != InvalidXLogRecPtr)
 		UpdateCheckPointDistanceEstimate(RedoRecPtr - PriorRedoPtr);
 
+#ifdef USE_INJECTION_POINTS
+	INJECTION_POINT("checkpoint-before-old-wal-removal");
+#endif
+
 	/*
 	 * Delete old log files, those no longer needed for last checkpoint to
 	 * prevent the disk holding the xlog from growing full.

src/backend/replication/logical/logical.c

@@ -30,6 +30,7 @@
 
 #include "access/xact.h"
 #include "access/xlogutils.h"
+#include "access/xlog_internal.h"
 #include "fmgr.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -41,6 +42,7 @@
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "utils/builtins.h"
+#include "utils/injection_point.h"
 #include "utils/inval.h"
 #include "utils/memutils.h"
 
@@ -1825,9 +1827,13 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
 	{
 		bool		updated_xmin = false;
 		bool		updated_restart = false;
+		XLogRecPtr	restart_lsn pg_attribute_unused();
 
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 
+		/* remember the old restart lsn */
+		restart_lsn = MyReplicationSlot->data.restart_lsn;
+
 		MyReplicationSlot->data.confirmed_flush = lsn;
 
 		/* if we're past the location required for bumping xmin, do so */
@@ -1869,6 +1875,18 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
 		/* first write new xmin to disk, so we know what's up after a crash */
 		if (updated_xmin || updated_restart)
 		{
+#ifdef USE_INJECTION_POINTS
+			XLogSegNo	seg1,
+						seg2;
+
+			XLByteToSeg(restart_lsn, seg1, wal_segment_size);
+			XLByteToSeg(MyReplicationSlot->data.restart_lsn, seg2, wal_segment_size);
+
+			/* trigger injection point, but only if segment changes */
+			if (seg1 != seg2)
+				INJECTION_POINT("logical-replication-slot-advance-segment");
+#endif
+
 			ReplicationSlotMarkDirty();
 			ReplicationSlotSave();
 			elog(DEBUG1, "updated xmin: %u restart: %u", updated_xmin, updated_restart);