Add system view pg_wait_events

This new view, wrapped around a SRF, shows some information known about
wait events, as of:
- Name.
- Type (Activity, I/O, Extension, etc.).
- Description.

All the information retrieved comes from wait_event_names.txt, and the
description is the same as the documentation with filters applied to
remove any XML markups.  This view is useful when joined with
pg_stat_activity to get the description of a wait event reported.

Custom wait events for extensions are included in the view.

Original idea by Yves Colin.

Author: Bertrand Drouvot
Reviewed-by: Kyotaro Horiguchi, Masahiro Ikeda, Tom Lane, Michael
Paquier
Discussion: https://postgr.es/m/0e2ae164-dc89-03c3-cf7f-de86378053ac@gmail.com

1 files changed, 93 insertions, 0 deletions

diff --git a/src/backend/utils/activity/wait_event_funcs.c b/src/backend/utils/activity/wait_event_funcs.c
new file mode 100644
index 00000000000..6a65f527048
--- /dev/null
+++ b/src/backend/utils/activity/wait_event_funcs.c
@@ -0,0 +1,93 @@
+/*------------------------------------------------------------------------
+ *
+ * wait_event_funcs.c
+ *	  Functions for accessing wait event data.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/activity/wait_event_funcs.c
+ *
+ *------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "funcapi.h"
+#include "utils/builtins.h"
+#include "utils/wait_event.h"
+
+/*
+ * Each wait event has one corresponding entry in this structure, fed to
+ * the SQL function of this file.
+ */
+static const struct
+{
+	const char *type;
+	const char *name;
+	const char *description;
+}
+
+			waitEventData[] =
+{
+#include "wait_event_funcs_data.c"
+	/* end of list */
+	{NULL, NULL, NULL}
+};
+
+
+/*
+ * pg_get_wait_events
+ *
+ * List information about wait events (type, name and description).
+ */
+Datum
+pg_get_wait_events(PG_FUNCTION_ARGS)
+{
+#define PG_GET_WAIT_EVENTS_COLS 3
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	char	  **waiteventnames;
+	int			nbextwaitevents;
+
+	/* Build tuplestore to hold the result rows */
+	InitMaterializedSRF(fcinfo, 0);
+
+	/* Iterate over the list of wait events */
+	for (int idx = 0; waitEventData[idx].type != NULL; idx++)
+	{
+		Datum		values[PG_GET_WAIT_EVENTS_COLS] = {0};
+		bool		nulls[PG_GET_WAIT_EVENTS_COLS] = {0};
+
+		values[0] = CStringGetTextDatum(waitEventData[idx].type);
+		values[1] = CStringGetTextDatum(waitEventData[idx].name);
+		values[2] = CStringGetTextDatum(waitEventData[idx].description);
+
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+	}
+
+	/* Handle custom wait events for extensions */
+	waiteventnames = GetWaitEventExtensionNames(&nbextwaitevents);
+
+	for (int idx = 0; idx < nbextwaitevents; idx++)
+	{
+		StringInfoData buf;
+		Datum		values[PG_GET_WAIT_EVENTS_COLS] = {0};
+		bool		nulls[PG_GET_WAIT_EVENTS_COLS] = {0};
+
+
+		values[0] = CStringGetTextDatum("Extension");
+		values[1] = CStringGetTextDatum(waiteventnames[idx]);
+
+		initStringInfo(&buf);
+		appendStringInfo(&buf,
+						 "Waiting for custom wait event \"%s\" defined by extension module",
+						 waiteventnames[idx]);
+
+		values[2] = CStringGetTextDatum(buf.data);
+
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+	}
+
+	return (Datum) 0;
+}