commit 908f3bb511450f05980ba01d42c909cc9ef8007a
Author: Daniel Gustafsson <dgustafsson@postgresql.org>
Date:   Thu Mar 14 14:32:15 2024 +0100

    Code review hackery

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 7d9ad9046f..115204f708 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -267,7 +267,7 @@ BackgroundWriterMain(void)
 		{
 			TimestampTz timeout = 0;
 			TimestampTz now = GetCurrentTimestamp();
-			XLogRecPtr	current_lsn = GetLastImportantRecPtr();
+			XLogRecPtr	current_lsn;
 
 			timeout = TimestampTzPlusMilliseconds(last_snapshot_ts,
 												  LOG_SNAPSHOT_INTERVAL_MS);
@@ -279,12 +279,15 @@ BackgroundWriterMain(void)
 			 * start of a record, whereas last_snapshot_lsn points just past
 			 * the end of the record.
 			 */
-			if (now >= timeout &&
-				last_snapshot_lsn <= current_lsn)
+			if (now >= timeout)
 			{
-				last_snapshot_lsn = LogStandbySnapshot();
-				last_snapshot_ts = now;
-				pgstat_wal_update_lsntimeline(now, current_lsn);
+				current_lsn = GetLastImportantRecPtr();
+				if (last_snapshot_lsn <= current_lsn)
+				{
+					last_snapshot_lsn = LogStandbySnapshot();
+					last_snapshot_ts = now;
+					pgstat_wal_update_lsntimeline(now, current_lsn);
+				}
 			}
 		}
 
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index 0a7b545fd2..90afec580b 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -238,7 +238,7 @@ lsntime_merge_target(LSNTimeline *timeline)
 	}
 
 	/* Should not be reachable or we are out of space */
-	Assert(false);
+	return -1;
 }
 
 /*
@@ -280,7 +280,12 @@ lsntime_insert(LSNTimeline *timeline, TimestampTz time,
 	 * down by one and insert the passed-in LSNTime at array index 0.
 	 */
 	merge_target = lsntime_merge_target(timeline);
-	Assert(merge_target >= 0 && merge_target < timeline->length);
+	if (merge_target < 0)
+	{
+		elog(WARNING, "unable to insert LSN in LSN timeline, merge failed");
+		return;
+	}
+	Assert(merge_target < timeline->length);
 	lsntime_merge(&timeline->data[merge_target], &timeline->data[merge_target - 1]);
 	memmove(&timeline->data[1], &timeline->data[0], sizeof(LSNTime) * merge_target - 1);
 	timeline->data[0] = entrant;