injection_points: Add some fixed-numbered statistics

Like 75534436a4, this acts mainly as a template to show what can be
achieved with fixed-numbered stats (like WAL, bgwriter, etc.) with the
pluggable cumulative statistics APIs introduced in 7949d95945.

Fixed-numbered stats are defined in their own file, named
injection_stats_fixed.c, separated entirely from the variable-numbered
case in injection_stats.c.  This is mainly for clarity as having both
examples in the same file would be confusing.

Note that this commit uses the helper routines added in 2eff9e678d.
The stats stored track globally the number of times injection points
have been attached, detached or run.  Two more fields should be added
later for the number of times a point has been cached or loaded, but
what's here is enough as a template.

More TAP tests are added, providing coverage for fixed-numbered custom
stats.

Author: Michael Paquier
Reviewed-by: Dmitry Dolgov, Bertrand Drouvot
Discussion: https://postgr.es/m/Zmqm9j5EO0I4W8dx@paquier.xyz

src/test/modules/injection_points/Makefile

@@ -4,7 +4,8 @@ MODULE_big = injection_points
 OBJS = \
 	$(WIN32RES) \
 	injection_points.o \
-	injection_stats.o
+	injection_stats.o \
+	injection_stats_fixed.o
 EXTENSION = injection_points
 DATA = injection_points--1.0.sql
 PGFILEDESC = "injection_points - facility for injection points"

src/test/modules/injection_points/injection_points--1.0.sql

@@ -84,3 +84,14 @@ CREATE FUNCTION injection_points_stats_numcalls(IN point_name TEXT)
 RETURNS bigint
 AS 'MODULE_PATHNAME', 'injection_points_stats_numcalls'
 LANGUAGE C STRICT;
+
+--
+-- injection_points_stats_fixed()
+--
+-- Reports fixed-numbered statistics for injection points.
+CREATE FUNCTION injection_points_stats_fixed(OUT numattach int8,
+   OUT numdetach int8,
+   OUT numrun int8)
+RETURNS record
+AS 'MODULE_PATHNAME', 'injection_points_stats_fixed'
+LANGUAGE C STRICT;

src/test/modules/injection_points/injection_points.c

@@ -297,6 +297,7 @@ injection_points_attach(PG_FUNCTION_ARGS)
 		condition.pid = MyProcPid;
 	}
 
+	pgstat_report_inj_fixed(1, 0, 0);
 	InjectionPointAttach(name, "injection_points", function, &condition,
 						 sizeof(InjectionPointCondition));
 
@@ -342,6 +343,7 @@ injection_points_run(PG_FUNCTION_ARGS)
 {
 	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
 
+	pgstat_report_inj_fixed(0, 0, 1);
 	INJECTION_POINT(name);
 
 	PG_RETURN_VOID();
@@ -432,6 +434,7 @@ injection_points_detach(PG_FUNCTION_ARGS)
 {
 	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
 
+	pgstat_report_inj_fixed(0, 1, 0);
 	if (!InjectionPointDetach(name))
 		elog(ERROR, "could not detach injection point \"%s\"", name);
 
@@ -459,4 +462,5 @@ _PG_init(void)
 		return;
 
 	pgstat_register_inj();
+	pgstat_register_inj_fixed();
 }

src/test/modules/injection_points/injection_stats.h

@@ -15,9 +15,16 @@
 #ifndef INJECTION_STATS
 #define INJECTION_STATS
 
+/* injection_stats.c */
 extern void pgstat_register_inj(void);
 extern void pgstat_create_inj(const char *name);
 extern void pgstat_drop_inj(const char *name);
 extern void pgstat_report_inj(const char *name);
 
+/* injection_stats_fixed.c */
+extern void pgstat_register_inj_fixed(void);
+extern void pgstat_report_inj_fixed(uint32 numattach,
+									uint32 numdetach,
+									uint32 numrun);
+
 #endif

src/test/modules/injection_points/injection_stats_fixed.c

@@ -0,0 +1,192 @@
+/*--------------------------------------------------------------------------
+ *
+ * injection_stats_fixed.c
+ *		Code for fixed-numbered statistics of injection points.
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/test/modules/injection_points/injection_stats_fixed.c
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "fmgr.h"
+
+#include "common/hashfn.h"
+#include "funcapi.h"
+#include "injection_stats.h"
+#include "pgstat.h"
+#include "utils/builtins.h"
+#include "utils/pgstat_internal.h"
+
+/* Structures for statistics of injection points, fixed-size */
+typedef struct PgStat_StatInjFixedEntry
+{
+	PgStat_Counter numattach;	/* number of points attached */
+	PgStat_Counter numdetach;	/* number of points detached */
+	PgStat_Counter numrun;		/* number of points run */
+	TimestampTz stat_reset_timestamp;
+} PgStat_StatInjFixedEntry;
+
+typedef struct PgStatShared_InjectionPointFixed
+{
+	LWLock		lock;			/* protects all the counters */
+	uint32		changecount;
+	PgStat_StatInjFixedEntry stats;
+	PgStat_StatInjFixedEntry reset_offset;
+} PgStatShared_InjectionPointFixed;
+
+/* Callbacks for fixed-numbered stats */
+static void injection_stats_fixed_init_shmem_cb(void *stats);
+static void injection_stats_fixed_reset_all_cb(TimestampTz ts);
+static void injection_stats_fixed_snapshot_cb(void);
+
+static const PgStat_KindInfo injection_stats_fixed = {
+	.name = "injection_points_fixed",
+	.fixed_amount = true,
+
+	.shared_size = sizeof(PgStat_StatInjFixedEntry),
+	.shared_data_off = offsetof(PgStatShared_InjectionPointFixed, stats),
+	.shared_data_len = sizeof(((PgStatShared_InjectionPointFixed *) 0)->stats),
+
+	.init_shmem_cb = injection_stats_fixed_init_shmem_cb,
+	.reset_all_cb = injection_stats_fixed_reset_all_cb,
+	.snapshot_cb = injection_stats_fixed_snapshot_cb,
+};
+
+/*
+ * Kind ID reserved for statistics of injection points.
+ */
+#define PGSTAT_KIND_INJECTION_FIXED	130
+
+/* Track if fixed-numbered stats are loaded */
+static bool inj_fixed_loaded = false;
+
+static void
+injection_stats_fixed_init_shmem_cb(void *stats)
+{
+	PgStatShared_InjectionPointFixed *stats_shmem =
+		(PgStatShared_InjectionPointFixed *) stats;
+
+	LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
+}
+
+static void
+injection_stats_fixed_reset_all_cb(TimestampTz ts)
+{
+	PgStatShared_InjectionPointFixed *stats_shmem =
+		pgstat_get_custom_shmem_data(PGSTAT_KIND_INJECTION_FIXED);
+
+	LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
+	pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,
+									&stats_shmem->stats,
+									sizeof(stats_shmem->stats),
+									&stats_shmem->changecount);
+	stats_shmem->stats.stat_reset_timestamp = ts;
+	LWLockRelease(&stats_shmem->lock);
+}
+
+static void
+injection_stats_fixed_snapshot_cb(void)
+{
+	PgStatShared_InjectionPointFixed *stats_shmem =
+		pgstat_get_custom_shmem_data(PGSTAT_KIND_INJECTION_FIXED);
+	PgStat_StatInjFixedEntry *stat_snap =
+		pgstat_get_custom_snapshot_data(PGSTAT_KIND_INJECTION_FIXED);
+	PgStat_StatInjFixedEntry *reset_offset = &stats_shmem->reset_offset;
+	PgStat_StatInjFixedEntry reset;
+
+	pgstat_copy_changecounted_stats(stat_snap,
+									&stats_shmem->stats,
+									sizeof(stats_shmem->stats),
+									&stats_shmem->changecount);
+
+	LWLockAcquire(&stats_shmem->lock, LW_SHARED);
+	memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));
+	LWLockRelease(&stats_shmem->lock);
+
+	/* compensate by reset offsets */
+#define FIXED_COMP(fld) stat_snap->fld -= reset.fld;
+	FIXED_COMP(numattach);
+	FIXED_COMP(numdetach);
+	FIXED_COMP(numrun);
+#undef FIXED_COMP
+}
+
+/*
+ * Workhorse to do the registration work, called in _PG_init().
+ */
+void
+pgstat_register_inj_fixed(void)
+{
+	pgstat_register_kind(PGSTAT_KIND_INJECTION_FIXED, &injection_stats_fixed);
+
+	/* mark stats as loaded */
+	inj_fixed_loaded = true;
+}
+
+/*
+ * Report fixed number of statistics for an injection point.
+ */
+void
+pgstat_report_inj_fixed(uint32 numattach,
+						uint32 numdetach,
+						uint32 numrun)
+{
+	PgStatShared_InjectionPointFixed *stats_shmem;
+
+	/* leave if disabled */
+	if (!inj_fixed_loaded)
+		return;
+
+	stats_shmem = pgstat_get_custom_shmem_data(PGSTAT_KIND_INJECTION_FIXED);
+
+	pgstat_begin_changecount_write(&stats_shmem->changecount);
+	stats_shmem->stats.numattach += numattach;
+	stats_shmem->stats.numdetach += numdetach;
+	stats_shmem->stats.numrun += numrun;
+	pgstat_end_changecount_write(&stats_shmem->changecount);
+}
+
+/*
+ * SQL function returning fixed-numbered statistics for injection points.
+ */
+PG_FUNCTION_INFO_V1(injection_points_stats_fixed);
+Datum
+injection_points_stats_fixed(PG_FUNCTION_ARGS)
+{
+	TupleDesc	tupdesc;
+	Datum		values[3] = {0};
+	bool		nulls[3] = {0};
+	PgStat_StatInjFixedEntry *stats;
+
+	if (!inj_fixed_loaded)
+		PG_RETURN_NULL();
+
+	pgstat_snapshot_fixed(PGSTAT_KIND_INJECTION_FIXED);
+	stats = pgstat_get_custom_snapshot_data(PGSTAT_KIND_INJECTION_FIXED);
+
+	/* Initialise attributes information in the tuple descriptor */
+	tupdesc = CreateTemplateTupleDesc(3);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "numattach",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "numdetach",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "numrun",
+					   INT8OID, -1, 0);
+	BlessTupleDesc(tupdesc);
+
+	values[0] = Int64GetDatum(stats->numattach);
+	values[1] = Int64GetDatum(stats->numdetach);
+	values[2] = Int64GetDatum(stats->numrun);
+	nulls[0] = false;
+	nulls[1] = false;
+	nulls[2] = false;
+
+	/* Returns the record as Datum */
+	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
+}

src/test/modules/injection_points/meson.build

@@ -7,6 +7,7 @@ endif
 injection_points_sources = files(
   'injection_points.c',
   'injection_stats.c',
+  'injection_stats_fixed.c',
 )
 
 if host_system == 'windows'

src/test/modules/injection_points/t/001_stats.pl

@@ -33,18 +33,27 @@ $node->safe_psql('postgres', "SELECT injection_points_run('stats-notice');");
 my $numcalls = $node->safe_psql('postgres',
 	"SELECT injection_points_stats_numcalls('stats-notice');");
 is($numcalls, '2', 'number of stats calls');
+my $fixedstats = $node->safe_psql('postgres',
+	"SELECT * FROM injection_points_stats_fixed();");
+is($fixedstats, '1|0|2', 'number of fixed stats');
 
 # Restart the node cleanly, stats should still be around.
 $node->restart;
 $numcalls = $node->safe_psql('postgres',
 	"SELECT injection_points_stats_numcalls('stats-notice');");
 is($numcalls, '2', 'number of stats after clean restart');
+$fixedstats = $node->safe_psql('postgres',
+	"SELECT * FROM injection_points_stats_fixed();");
+is($fixedstats, '1|0|2', 'number of fixed stats after clean restart');
 
 # On crash the stats are gone.
 $node->stop('immediate');
 $node->start;
 $numcalls = $node->safe_psql('postgres',
 	"SELECT injection_points_stats_numcalls('stats-notice');");
-is($numcalls, '', 'number of stats after clean restart');
+is($numcalls, '', 'number of stats after crash');
+$fixedstats = $node->safe_psql('postgres',
+	"SELECT * FROM injection_points_stats_fixed();");
+is($fixedstats, '0|0|0', 'number of fixed stats after crash');
 
 done_testing();

src/tools/pgindent/typedefs.list

@@ -2120,6 +2120,7 @@ PgStatShared_Database
 PgStatShared_Function
 PgStatShared_HashEntry
 PgStatShared_InjectionPoint
+PgStatShared_InjectionPointFixed
 PgStatShared_IO
 PgStatShared_Relation
 PgStatShared_ReplSlot
@@ -2152,6 +2153,7 @@ PgStat_SnapshotEntry
 PgStat_StatDBEntry
 PgStat_StatFuncEntry
 PgStat_StatInjEntry
+PgStat_StatInjFixedEntry
 PgStat_StatReplSlotEntry
 PgStat_StatSubEntry
 PgStat_StatTabEntry