Rename some pgstats callbacks related to flush of entries

The two callbacks have_fixed_pending_cb and flush_fixed_cb have been
introduced in fc415edf8ca8 to provide a way for fixed-numbered
statistics to control the flush of their data.  These are renamed to
respectively have_static_pending_cb and flush_static_cb.  The
restriction that these only apply to fixed-numbered stats is removed.

A follow-up patch will make use of them for backend statistics.  This
stats kind is variable-numbered, and patches are under discussion to
track WAL data for IO and backend stats which cannot use
PgStat_EntryRef->pending as pending data would be touched in critical
sections, where no memory allocation can happen.

Per discussion with Andres Freund.

Author: Bertrand Drouvot
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/66efowskppsns35v5u2m7k4sdnl7yoz5bo64tdjwq7r5lhplrz@y7dme5xwh2r5

1 files changed, 17 insertions, 10 deletions

diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 4bb8e5c53ab..8914aaca9ab 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -156,8 +156,8 @@ typedef struct PgStat_EntryRef
 	 * Pending statistics data that will need to be flushed to shared memory
 	 * stats eventually. Each stats kind utilizing pending data defines what
 	 * format its pending data has and needs to provide a
-	 * PgStat_KindInfo->flush_pending_cb callback to merge pending into shared
-	 * stats.
+	 * PgStat_KindInfo->flush_pending_cb callback to merge pending entries
+	 * into the shared stats hash table.
 	 */
 	void	   *pending;
 	dlist_node	pending_node;	/* membership in pgStatPending list */
@@ -260,7 +260,8 @@ typedef struct PgStat_KindInfo
 
 	/*
 	 * For variable-numbered stats: flush pending stats. Required if pending
-	 * data is used.  See flush_fixed_cb for fixed-numbered stats.
+	 * data is used. See flush_static_cb when dealing with stats data that
+	 * that cannot use PgStat_EntryRef->pending.
 	 */
 	bool		(*flush_pending_cb) (PgStat_EntryRef *sr, bool nowait);
 
@@ -289,17 +290,23 @@ typedef struct PgStat_KindInfo
 	void		(*init_shmem_cb) (void *stats);
 
 	/*
-	 * For fixed-numbered statistics: Flush pending stats. Returns true if
-	 * some of the stats could not be flushed, due to lock contention for
-	 * example. Optional.
+	 * For fixed-numbered or variable-numbered statistics: Flush pending stats
+	 * entries, for stats kinds that do not use PgStat_EntryRef->pending.
+	 *
+	 * Returns true if some of the stats could not be flushed, due to lock
+	 * contention for example. Optional.
 	 */
-	bool		(*flush_fixed_cb) (bool nowait);
+	bool		(*flush_static_cb) (bool nowait);
 
 	/*
-	 * For fixed-numbered statistics: Check for pending stats in need of
-	 * flush. Returns true if there are any stats pending for flush. Optional.
+	 * For fixed-numbered or variable-numbered statistics: Check for pending
+	 * stats in need of flush with flush_static_cb, when these do not use
+	 * PgStat_EntryRef->pending.
+	 *
+	 * Returns true if there are any stats pending for flush, triggering
+	 * flush_static_cb. Optional.
 	 */
-	bool		(*have_fixed_pending_cb) (void);
+	bool		(*have_static_pending_cb) (void);
 
 	/*
 	 * For fixed-numbered statistics: Reset All.