Rename some support functions for pgstat* views.

Presently, pgstat_fetch_stat_beentry() accepts a session's backend
ID as its argument, and pgstat_fetch_stat_local_beentry() accepts a
1-based index in an internal array as its argument.  The former is
typically used wherever a user must provide a backend ID, and the
latter is usually used internally when looping over all entries in
the array.  This difference was first introduced by d7e39d7.
Before that commit, both functions accepted a 1-based index to the
internal array.

This commit renames these two functions to make it clear whether
they use the backend ID or the 1-based index to look up the entry.
This is preparatory work for a follow-up change that will introduce
a function for looking up a LocalPgBackendStatus using a backend
ID.

Reviewed-by: Ian Barwick, Sami Imseih, Michael Paquier, Robert Haas
Discussion: https://postgr.es/m/CAB8KJ%3Dj-ACb3H4L9a_b3ZG3iCYDW5aEu3WsPAzkm2S7JzS1Few%40mail.gmail.com
Backpatch-through: 16

Author: nathan-bossart

src/backend/utils/activity/backend_status.c

@@ -849,8 +849,8 @@ pgstat_read_current_status(void)
 			/*
 			 * The BackendStatusArray index is exactly the BackendId of the
 			 * source backend.  Note that this means localBackendStatusTable
-			 * is in order by backend_id.  pgstat_fetch_stat_beentry() depends
-			 * on that.
+			 * is in order by backend_id.  pgstat_get_beentry_by_backend_id()
+			 * depends on that.
 			 */
 			localentry->backend_id = i;
 			BackendIdGetTransactionIds(i,
@@ -1073,21 +1073,21 @@ cmp_lbestatus(const void *a, const void *b)
 }
 
 /* ----------
- * pgstat_fetch_stat_beentry() -
+ * pgstat_get_beentry_by_backend_id() -
  *
  *	Support function for the SQL-callable pgstat* functions. Returns
  *	our local copy of the current-activity entry for one backend,
  *	or NULL if the given beid doesn't identify any known session.
  *
  *	The beid argument is the BackendId of the desired session
- *	(note that this is unlike pgstat_fetch_stat_local_beentry()).
+ *	(note that this is unlike pgstat_get_local_beentry_by_index()).
  *
  *	NB: caller is responsible for a check if the user is permitted to see
  *	this info (especially the querystring).
  * ----------
  */
 PgBackendStatus *
-pgstat_fetch_stat_beentry(BackendId beid)
+pgstat_get_beentry_by_backend_id(BackendId beid)
 {
 	LocalPgBackendStatus key;
 	LocalPgBackendStatus *ret;
@@ -1111,28 +1111,28 @@ pgstat_fetch_stat_beentry(BackendId beid)
 
 
 /* ----------
- * pgstat_fetch_stat_local_beentry() -
+ * pgstat_get_local_beentry_by_index() -
  *
- *	Like pgstat_fetch_stat_beentry() but with locally computed additions (like
- *	xid and xmin values of the backend)
+ *	Like pgstat_get_beentry_by_backend_id() but with locally computed additions
+ *	(like xid and xmin values of the backend)
  *
- *	The beid argument is a 1-based index in the localBackendStatusTable
- *	(note that this is unlike pgstat_fetch_stat_beentry()).
+ *	The idx argument is a 1-based index in the localBackendStatusTable
+ *	(note that this is unlike pgstat_get_beentry_by_backend_id()).
  *	Returns NULL if the argument is out of range (no current caller does that).
  *
  *	NB: caller is responsible for a check if the user is permitted to see
  *	this info (especially the querystring).
  * ----------
  */
 LocalPgBackendStatus *
-pgstat_fetch_stat_local_beentry(int beid)
+pgstat_get_local_beentry_by_index(int idx)
 {
 	pgstat_read_current_status();
 
-	if (beid < 1 || beid > localNumBackends)
+	if (idx < 1 || idx > localNumBackends)
 		return NULL;
 
-	return &localBackendStatusTable[beid - 1];
+	return &localBackendStatusTable[idx - 1];
 }
 
 
@@ -1141,7 +1141,7 @@ pgstat_fetch_stat_local_beentry(int beid)
  *
  *	Support function for the SQL-callable pgstat* functions. Returns
  *	the number of sessions known in the localBackendStatusTable, i.e.
- *	the maximum 1-based index to pass to pgstat_fetch_stat_local_beentry().
+ *	the maximum 1-based index to pass to pgstat_get_local_beentry_by_index().
  * ----------
  */
 int

src/backend/utils/adt/pgstatfuncs.c

@@ -211,7 +211,7 @@ pg_stat_get_backend_idset(PG_FUNCTION_ARGS)
 	if (fctx[0] <= pgstat_fetch_stat_numbackends())
 	{
 		/* do when there is more left to send */
-		LocalPgBackendStatus *local_beentry = pgstat_fetch_stat_local_beentry(fctx[0]);
+		LocalPgBackendStatus *local_beentry = pgstat_get_local_beentry_by_index(fctx[0]);
 
 		SRF_RETURN_NEXT(funcctx, Int32GetDatum(local_beentry->backend_id));
 	}
@@ -264,7 +264,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 		bool		nulls[PG_STAT_GET_PROGRESS_COLS] = {0};
 		int			i;
 
-		local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
+		local_beentry = pgstat_get_local_beentry_by_index(curr_backend);
 		beentry = &local_beentry->backendStatus;
 
 		/*
@@ -325,7 +325,7 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		const char *wait_event = NULL;
 
 		/* Get the next one in the list */
-		local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
+		local_beentry = pgstat_get_local_beentry_by_index(curr_backend);
 		beentry = &local_beentry->backendStatus;
 
 		/* If looking for specific PID, ignore all the others */
@@ -672,7 +672,7 @@ pg_stat_get_backend_pid(PG_FUNCTION_ARGS)
 	int32		beid = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_INT32(beentry->st_procpid);
@@ -685,7 +685,7 @@ pg_stat_get_backend_dbid(PG_FUNCTION_ARGS)
 	int32		beid = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_OID(beentry->st_databaseid);
@@ -698,7 +698,7 @@ pg_stat_get_backend_userid(PG_FUNCTION_ARGS)
 	int32		beid = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_OID(beentry->st_userid);
@@ -727,7 +727,7 @@ pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
 
 	BlessTupleDesc(tupdesc);
 
-	if ((local_beentry = pgstat_fetch_stat_local_beentry(beid)) != NULL)
+	if ((local_beentry = pgstat_get_local_beentry_by_index(beid)) != NULL)
 	{
 		/* Fill values and NULLs */
 		values[0] = Int32GetDatum(local_beentry->backend_subxact_count);
@@ -752,7 +752,7 @@ pg_stat_get_backend_activity(PG_FUNCTION_ARGS)
 	char	   *clipped_activity;
 	text	   *ret;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		activity = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		activity = "<insufficient privilege>";
@@ -776,7 +776,7 @@ pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS)
 	PGPROC	   *proc;
 	const char *wait_event_type = NULL;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		wait_event_type = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		wait_event_type = "<insufficient privilege>";
@@ -797,7 +797,7 @@ pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS)
 	PGPROC	   *proc;
 	const char *wait_event = NULL;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		wait_event = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		wait_event = "<insufficient privilege>";
@@ -818,7 +818,7 @@ pg_stat_get_backend_activity_start(PG_FUNCTION_ARGS)
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -844,7 +844,7 @@ pg_stat_get_backend_xact_start(PG_FUNCTION_ARGS)
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -866,7 +866,7 @@ pg_stat_get_backend_start(PG_FUNCTION_ARGS)
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -890,7 +890,7 @@ pg_stat_get_backend_client_addr(PG_FUNCTION_ARGS)
 	char		remote_host[NI_MAXHOST];
 	int			ret;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -935,7 +935,7 @@ pg_stat_get_backend_client_port(PG_FUNCTION_ARGS)
 	char		remote_port[NI_MAXSERV];
 	int			ret;
 
-	if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -978,12 +978,12 @@ pg_stat_get_db_numbackends(PG_FUNCTION_ARGS)
 	Oid			dbid = PG_GETARG_OID(0);
 	int32		result;
 	int			tot_backends = pgstat_fetch_stat_numbackends();
-	int			beid;
+	int			idx;
 
 	result = 0;
-	for (beid = 1; beid <= tot_backends; beid++)
+	for (idx = 1; idx <= tot_backends; idx++)
 	{
-		LocalPgBackendStatus *local_beentry = pgstat_fetch_stat_local_beentry(beid);
+		LocalPgBackendStatus *local_beentry = pgstat_get_local_beentry_by_index(idx);
 
 		if (local_beentry->backendStatus.st_databaseid == dbid)
 			result++;

src/include/utils/backend_status.h

@@ -333,8 +333,8 @@ extern uint64 pgstat_get_my_query_id(void);
  * ----------
  */
 extern int	pgstat_fetch_stat_numbackends(void);
-extern PgBackendStatus *pgstat_fetch_stat_beentry(BackendId beid);
-extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
+extern PgBackendStatus *pgstat_get_beentry_by_backend_id(BackendId beid);
+extern LocalPgBackendStatus *pgstat_get_local_beentry_by_index(int idx);
 extern char *pgstat_clip_activity(const char *raw_activity);