Adjust log level of logical decoding messages by context

Commit 21b018e7ea lowered some logical decoding messages from LOG to DEBUG1.
However, per discussion on pgsql-hackers, messages from background activity
(e.g., walsender or slotsync worker) should remain at LOG, as they are less
frequent and more likely to indicate issues that DBAs should notice.

For foreground SQL functions (e.g., pg_logical_slot_peek_binary_changes()),
keep these messages at DEBUG1 to avoid excessive log noise. They can still be
enabled by lowering client_min_messages or log_min_messages for the session.

This commit updates logical decoding to log these messages at LOG for
background activity and at DEBUG1 for foreground execution.

Suggested-by: Robert Haas <robertmhaas@gmail.com>
Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CA+TgmoYsu2+YAo9eLGkDp5VP-pfQ-jOoX382vS4THKHeRTNgew@mail.gmail.com

src/backend/replication/logical/logical.c

@@ -603,7 +603,7 @@ CreateDecodingContext(XLogRecPtr start_lsn,
 
 	ctx->reorder->output_rewrites = ctx->options.receive_rewrites;
 
-	ereport(DEBUG1,
+	ereport(LogicalDecodingLogLevel(),
 			(errmsg("starting logical decoding for slot \"%s\"",
 					NameStr(slot->data.name)),
 			 errdetail("Streaming transactions committing after %X/%08X, reading WAL from %X/%08X.",

src/backend/replication/logical/snapbuild.c

@@ -1365,7 +1365,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
 
-		ereport(DEBUG1,
+		ereport(LogicalDecodingLogLevel(),
 				errmsg("logical decoding found consistent point at %X/%08X",
 					   LSN_FORMAT_ARGS(lsn)),
 				errdetail("There are no running transactions."));
@@ -1462,7 +1462,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
 
-		ereport(DEBUG1,
+		ereport(LogicalDecodingLogLevel(),
 				errmsg("logical decoding found consistent point at %X/%08X",
 					   LSN_FORMAT_ARGS(lsn)),
 				errdetail("There are no old transactions anymore."));
@@ -1972,7 +1972,7 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 
 	Assert(builder->state == SNAPBUILD_CONSISTENT);
 
-	ereport(DEBUG1,
+	ereport(LogicalDecodingLogLevel(),
 			errmsg("logical decoding found consistent point at %X/%08X",
 				   LSN_FORMAT_ARGS(lsn)),
 			errdetail("Logical decoding will begin using saved snapshot."));

src/include/replication/logical.h

@@ -154,4 +154,25 @@ extern XLogRecPtr LogicalReplicationSlotCheckPendingWal(XLogRecPtr end_of_wal,
 extern XLogRecPtr LogicalSlotAdvanceAndCheckSnapState(XLogRecPtr moveto,
 													  bool *found_consistent_snapshot);
 
+
+/*
+ * This macro determines the log level for messages about starting logical
+ * decoding and finding a consistent point.
+ *
+ * When logical decoding is triggered by a foreground SQL function (e.g.,
+ * pg_logical_slot_peek_binary_changes()), these messages are logged at DEBUG1
+ * to avoid excessive log noise. This is acceptable since such issues are
+ * typically less critical, and the messages can still be enabled by lowering
+ * client_min_messages or log_min_messages for the session.
+ *
+ * When the messages originate from background activity (e.g., walsender or
+ * slotsync worker), they are logged at LOG, as these events are less frequent
+ * and more likely to indicate issues that DBAs should notice by default.
+ *
+ * Note that SQL functions executed by the logical walsender are treated as
+ * background activity.
+ */
+#define LogicalDecodingLogLevel() \
+	(AmRegularBackendProcess() ? DEBUG1 : LOG)
+
 #endif

src/test/recovery/t/038_save_logical_slots_shutdown.pl

@@ -48,7 +48,6 @@ $node_publisher->append_conf(
 	'postgresql.conf', q{
 checkpoint_timeout = 1h
 autovacuum = off
-log_min_messages = 'debug1'
 });
 $node_publisher->start;