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

diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index 34520535d5491908d5e391fb4890e810b565bf7d..402e8202bfaee06d8b3ef27d25655494d3d4ef42 100644 (file)
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -437,8 +437,8 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
        .shared_data_off = offsetof(PgStatShared_IO, stats),
        .shared_data_len = sizeof(((PgStatShared_IO *) 0)->stats),
 
-       .flush_fixed_cb = pgstat_io_flush_cb,
-       .have_fixed_pending_cb = pgstat_io_have_pending_cb,
+       .flush_static_cb = pgstat_io_flush_cb,
+       .have_static_pending_cb = pgstat_io_have_pending_cb,
        .init_shmem_cb = pgstat_io_init_shmem_cb,
        .reset_all_cb = pgstat_io_reset_all_cb,
        .snapshot_cb = pgstat_io_snapshot_cb,
@@ -455,8 +455,8 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
        .shared_data_off = offsetof(PgStatShared_SLRU, stats),
        .shared_data_len = sizeof(((PgStatShared_SLRU *) 0)->stats),
 
-       .flush_fixed_cb = pgstat_slru_flush_cb,
-       .have_fixed_pending_cb = pgstat_slru_have_pending_cb,
+       .flush_static_cb = pgstat_slru_flush_cb,
+       .have_static_pending_cb = pgstat_slru_have_pending_cb,
        .init_shmem_cb = pgstat_slru_init_shmem_cb,
        .reset_all_cb = pgstat_slru_reset_all_cb,
        .snapshot_cb = pgstat_slru_snapshot_cb,
@@ -474,8 +474,8 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
        .shared_data_len = sizeof(((PgStatShared_Wal *) 0)->stats),
 
        .init_backend_cb = pgstat_wal_init_backend_cb,
-       .flush_fixed_cb = pgstat_wal_flush_cb,
-       .have_fixed_pending_cb = pgstat_wal_have_pending_cb,
+       .flush_static_cb = pgstat_wal_flush_cb,
+       .have_static_pending_cb = pgstat_wal_have_pending_cb,
        .init_shmem_cb = pgstat_wal_init_shmem_cb,
        .reset_all_cb = pgstat_wal_reset_all_cb,
        .snapshot_cb = pgstat_wal_snapshot_cb,
@@ -713,22 +713,17 @@ pgstat_report_stat(bool force)
    {
        bool        do_flush = false;
 
-       /* Check for pending fixed-numbered stats */
+       /* Check for pending stats */
        for (PgStat_Kind kind = PGSTAT_KIND_MIN; kind <= PGSTAT_KIND_MAX; kind++)
        {
            const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
            if (!kind_info)
                continue;
-           if (!kind_info->fixed_amount)
-           {
-               Assert(kind_info->have_fixed_pending_cb == NULL);
-               continue;
-           }
-           if (!kind_info->have_fixed_pending_cb)
+           if (!kind_info->have_static_pending_cb)
                continue;
 
-           if (kind_info->have_fixed_pending_cb())
+           if (kind_info->have_static_pending_cb())
            {
                do_flush = true;
                break;
@@ -789,25 +784,20 @@ pgstat_report_stat(bool force)
 
    partial_flush = false;
 
-   /* flush of variable-numbered stats */
+   /* flush of variable-numbered stats tracked in pending entries list */
    partial_flush |= pgstat_flush_pending_entries(nowait);
 
-   /* flush of fixed-numbered stats */
+   /* flush of other stats kinds */
    for (PgStat_Kind kind = PGSTAT_KIND_MIN; kind <= PGSTAT_KIND_MAX; kind++)
    {
        const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
        if (!kind_info)
            continue;
-       if (!kind_info->fixed_amount)
-       {
-           Assert(kind_info->flush_fixed_cb == NULL);
-           continue;
-       }
-       if (!kind_info->flush_fixed_cb)
+       if (!kind_info->flush_static_cb)
            continue;
 
-       partial_flush |= kind_info->flush_fixed_cb(nowait);
+       partial_flush |= kind_info->flush_static_cb(nowait);
    }
 
    last_flush = now;

diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 4bb8e5c53ab2fcd5b65e26c243f7a181b20395f0..8914aaca9ab93052d9e81ed29152966b319c9070 100644 (file)
--- 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.