Refactor code of pg_stat_get_wal() building result tuple

This commit adds to pgstatfuncs.c a new routine called
pg_stat_wal_build_tuple(), helper routine for pg_stat_get_wal().  This
is in charge of filling one tuple based on the contents of
PgStat_WalStats retrieved from pgstats.

This refactoring will be used by an upcoming patch introducing
backend-level WAL statistics, simplifying the main patch.  Note that
it is not possible for stats_reset to be NULL in pg_stat_wal; backend
statistics need to be able to handle this case.

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

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0ea41299e07966896d07614e30b5752fae9f309f..efb6d0032afe726b5a6d0d40861f499982ee83d7 100644 (file)
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1632,21 +1632,23 @@ 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_counters.
  */
-Datum
-pg_stat_get_wal(PG_FUNCTION_ARGS)
+static Datum
+pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
+                       TimestampTz stat_reset_timestamp)
 {
-#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;
-   PgStat_WalCounters wal_counters;
 
    /* 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",
@@ -1660,10 +1662,6 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 
    BlessTupleDesc(tupdesc);
 
-   /* 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_counters.wal_records);
    values[1] = Int64GetDatum(wal_counters.wal_fpi);
@@ -1677,12 +1675,30 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 
    values[3] = Int64GetDatum(wal_counters.wal_buffers_full);
 
-   values[4] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+   if (stat_reset_timestamp != 0)
+       values[4] = TimestampTzGetDatum(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->wal_counters,
+                                   wal_stats->stat_reset_timestamp));
+}
+
 /*
  * Returns statistics of SLRU caches.
  */