Adding new PgStat_WalCounters structure in pgstat.h

This new structure contains the counters and the data related to the WAL
activity statistics gathered from WalUsage, separated into its own
structure so as it can be shared across more than one Stats structure in
pg_stat.h.

This refactoring will be used by an upcoming patch introducing
backend-level WAL statistics.

Bump PGSTAT_FILE_FORMAT_ID.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/Z3zqc4o09dM/Ezyz@ip-10-97-1-34.eu-west-3.compute.internal

Author: michaelpq

src/backend/utils/activity/pgstat_wal.c

@@ -106,7 +106,7 @@ pgstat_wal_flush_cb(bool nowait)
 		return true;
 
 #define WALSTAT_ACC(fld, var_to_add) \
-	(stats_shmem->stats.fld += var_to_add.fld)
+	(stats_shmem->stats.wal_counters.fld += var_to_add.fld)
 	WALSTAT_ACC(wal_records, wal_usage_diff);
 	WALSTAT_ACC(wal_fpi, wal_usage_diff);
 	WALSTAT_ACC(wal_bytes, wal_usage_diff);

src/backend/utils/adt/pgstatfuncs.c

@@ -1643,6 +1643,7 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 	bool		nulls[PG_STAT_GET_WAL_COLS] = {0};
 	char		buf[256];
 	PgStat_WalStats *wal_stats;
+	PgStat_WalCounters wal_counters;
 
 	/* Initialise attributes information in the tuple descriptor */
 	tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_WAL_COLS);
@@ -1661,19 +1662,20 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 
 	/* Get statistics about WAL activity */
 	wal_stats = pgstat_fetch_stat_wal();
+	wal_counters = wal_stats->wal_counters;
 
 	/* Fill values and NULLs */
-	values[0] = Int64GetDatum(wal_stats->wal_records);
-	values[1] = Int64GetDatum(wal_stats->wal_fpi);
+	values[0] = Int64GetDatum(wal_counters.wal_records);
+	values[1] = Int64GetDatum(wal_counters.wal_fpi);
 
 	/* Convert to numeric. */
-	snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats->wal_bytes);
+	snprintf(buf, sizeof buf, UINT64_FORMAT, wal_counters.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_counters.wal_buffers_full);
 
 	values[4] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
 

src/include/pgstat.h

@@ -212,7 +212,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB4
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB5
 
 typedef struct PgStat_ArchiverStats
 {
@@ -474,12 +474,29 @@ typedef struct PgStat_StatTabEntry
 	PgStat_Counter total_autoanalyze_time;
 } PgStat_StatTabEntry;
 
-typedef struct PgStat_WalStats
+/* ------
+ * PgStat_WalCounters	WAL activity data gathered from WalUsage
+ *
+ * This stores all the counters and data gathered from WalUsage for WAL
+ * activity statistics, separated into its own structure so as this can be
+ * shared across multiple Stats structures.
+ * ------
+ */
+typedef struct PgStat_WalCounters
 {
 	PgStat_Counter wal_records;
 	PgStat_Counter wal_fpi;
 	uint64		wal_bytes;
 	PgStat_Counter wal_buffers_full;
+} PgStat_WalCounters;
+
+/* -------
+ * PgStat_WalStats		WAL statistics
+ * -------
+ */
+typedef struct PgStat_WalStats
+{
+	PgStat_WalCounters wal_counters;
 	TimestampTz stat_reset_timestamp;
 } PgStat_WalStats;
 

src/tools/pgindent/typedefs.list

@@ -2189,6 +2189,7 @@ PgStat_SubXactStatus
 PgStat_TableCounts
 PgStat_TableStatus
 PgStat_TableXactStatus
+PgStat_WalCounters
 PgStat_WalStats
 PgXmlErrorContext
 PgXmlStrictness