Return NULL in pg_get_snapshot_timestamp function instead of 1/01/1970

Author: knizhnik

src/backend/storage/file/fd.c

@@ -3960,6 +3960,7 @@ sfs_snapshot_file_size(const char *fname, bool isdir, int elevel)
 int64
 sfs_get_snapshot_size(SnapshotId snap_id)
 {
+	sfs_check_snapshot(snap_id);
 	sfs_snapshot_size = 0;
 	sfs_current_snapshot = snap_id;
 	walk_data_dir(sfs_snapshot_file_size, LOG);
@@ -3991,13 +3992,14 @@ sfs_snapshot_file_time(const char *fname, bool isdir, int elevel)
 	}
 }
 
-TimestampTz
+time_t
 sfs_get_snapshot_timestamp(SnapshotId snap_id)
 {
+	sfs_check_snapshot(snap_id);
 	sfs_snapshot_time = -1;
 	sfs_current_snapshot = snap_id;
 	walk_data_dir(sfs_snapshot_file_time, LOG);
-	return time_t_to_timestamptz((time_t)sfs_snapshot_time);
+	return sfs_snapshot_time;
 }
 
 void

src/backend/storage/file/snapfs.c

@@ -293,6 +293,10 @@ Datum pg_get_backend_snapshot(PG_FUNCTION_ARGS)
 Datum pg_get_snapshot_timestamp(PG_FUNCTION_ARGS)
 {
 	SnapshotId snap_id = PG_GETARG_INT32(0);
-	PG_RETURN_TIMESTAMPTZ(sfs_get_snapshot_timestamp(snap_id));
+    time_t t = sfs_get_snapshot_timestamp(snap_id);
+	if (t == (time_t)-1)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_TIMESTAMPTZ(time_t_to_timestamptz(t));
 }
 

src/backend/utils/misc/guc.c

@@ -3070,7 +3070,7 @@ static struct config_int ConfigureNamesInt[] =
 			gettext_noop("Sets active snapfs snapshot."),
 			NULL,
 		},
-		&sfs_active_snapshot,
+		(int*)&sfs_active_snapshot,
 		-1, -1, INT_MAX,
 		NULL, NULL, NULL
 	},

src/include/storage/snapfs.h

@@ -54,7 +54,7 @@ extern int64 sfs_get_snapshot_size(SnapshotId sid);
 /*
  * Get snapshot timestamp (time of first database modification in this snapshot)
  */
-extern TimestampTz sfs_get_snapshot_timestamp(SnapshotId sid);
+extern time_t sfs_get_snapshot_timestamp(SnapshotId sid);
 
 /*
  * Iternal functions and variables