From f2c3f83228e0cb1909cdd43f732ecaa377e0ebeb Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Mon, 6 Jan 2025 07:51:27 +0000
Subject: [PATCH v9 2/5] Extract logic filling pg_stat_get_wal()'s tuple into
 its own routine

This commit adds pg_stat_wal_build_tuple(), a helper routine for
pg_stat_get_wal(), that fills its tuple based on the contents
of PgStat_WalStats.  This will be used in a follow-up commit that uses
the same structures as pg_stat_wal for reporting, but for the PGSTAT_KIND_BACKEND
statistics kind.
---
 src/backend/utils/adt/pgstatfuncs.c | 48 +++++++++++++++++++----------
 1 file changed, 32 insertions(+), 16 deletions(-)
 100.0% src/backend/utils/adt/

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 68e16e52ab6..620d60a0938 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1632,20 +1632,22 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
 }
 
 /*
- * Returns statistics of WAL activity
+ * pg_stat_wal_build_tuple
+ *
+ * Helper routine for pg_stat_get_wal() returning one tuple based on the contents
+ * of wal_stats.
  */
-Datum
-pg_stat_get_wal(PG_FUNCTION_ARGS)
+static Datum
+pg_stat_wal_build_tuple(PgStat_WalStats wal_stats)
 {
-#define PG_STAT_GET_WAL_COLS	5
+#define PG_STAT_WAL_COLS	5
 	TupleDesc	tupdesc;
-	Datum		values[PG_STAT_GET_WAL_COLS] = {0};
-	bool		nulls[PG_STAT_GET_WAL_COLS] = {0};
+	Datum		values[PG_STAT_WAL_COLS] = {0};
+	bool		nulls[PG_STAT_WAL_COLS] = {0};
 	char		buf[256];
-	PgStat_WalStats *wal_stats;
 
 	/* Initialise attributes information in the tuple descriptor */
-	tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_WAL_COLS);
+	tupdesc = CreateTemplateTupleDesc(PG_STAT_WAL_COLS);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "wal_records",
 					   INT8OID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "wal_fpi",
@@ -1659,28 +1661,42 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 
 	BlessTupleDesc(tupdesc);
 
-	/* Get statistics about WAL activity */
-	wal_stats = pgstat_fetch_stat_wal();
-
 	/* Fill values and NULLs */
-	values[0] = Int64GetDatum(wal_stats->wal_records);
-	values[1] = Int64GetDatum(wal_stats->wal_fpi);
+	values[0] = Int64GetDatum(wal_stats.wal_records);
+	values[1] = Int64GetDatum(wal_stats.wal_fpi);
 
 	/* Convert to numeric. */
-	snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats->wal_bytes);
+	snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats.wal_bytes);
 	values[2] = DirectFunctionCall3(numeric_in,
 									CStringGetDatum(buf),
 									ObjectIdGetDatum(0),
 									Int32GetDatum(-1));
 
-	values[3] = Int64GetDatum(wal_stats->wal_buffers_full);
+	values[3] = Int64GetDatum(wal_stats.wal_buffers_full);
 
-	values[4] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+	if (wal_stats.stat_reset_timestamp != 0)
+		values[4] = TimestampTzGetDatum(wal_stats.stat_reset_timestamp);
+	else
+		nulls[4] = true;
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
 }
 
+/*
+ * Returns statistics of WAL activity
+ */
+Datum
+pg_stat_get_wal(PG_FUNCTION_ARGS)
+{
+	PgStat_WalStats *wal_stats;
+
+	/* Get statistics about WAL activity */
+	wal_stats = pgstat_fetch_stat_wal();
+
+	return (pg_stat_wal_build_tuple(*wal_stats));
+}
+
 /*
  * Returns statistics of SLRU caches.
  */
-- 
2.34.1