Re: shared-memory based stats collector - Mailing list pgsql-hackers

At Mon, 22 Mar 2021 09:55:59 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> At Thu, 18 Mar 2021 01:47:20 -0700, Andres Freund <andres@anarazel.de> wrote in 
> > Hi,
> > 
> > On 2021-03-18 16:56:02 +0900, Kyotaro Horiguchi wrote:
> > > At Tue, 16 Mar 2021 10:27:55 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> > > Rebased and fixed two bugs.  Not addressed received comments in this
> > > version.
> > 
> > Since I am heavily editing the code, could you submit "functional"
> > changes (as opposed to fixing rebase issues) as incremental patches?
> 
> Oh.. please wait for.. a moment, maybe.

This is that.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index c09fa026b9..3f546afe6a 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1175,13 +1175,6 @@ pgstat_report_stat(bool force)
     if (area == NULL)
         return 0;
 
-    /*
-     * We need a database entry if the following stats exists.
-     */
-    if (pgStatXactCommit > 0 || pgStatXactRollback > 0 ||
-        pgStatBlockReadTime > 0 || pgStatBlockWriteTime > 0)
-        get_local_dbstat_entry(MyDatabaseId);
-
     /* Don't expend a clock check if nothing to do */
     if (pgStatLocalHash == NULL && have_slrustats && !walstats_pending())
         return 0;
@@ -1221,8 +1214,6 @@ pgstat_report_stat(bool force)
     {
         int            remains = 0;
         pgstat_localhash_iterator i;
-        List       *dbentlist = NIL;
-        ListCell   *lc;
         PgStatLocalHashEntry *lent;
 
         /* Step 1: flush out other than database stats */
@@ -1234,13 +1225,11 @@ pgstat_report_stat(bool force)
             switch (lent->key.type)
             {
                 case PGSTAT_TYPE_DB:
-
                     /*
                      * flush_tabstat applies some of stats numbers of flushed
-                     * entries into local database stats. Just remember the
-                     * database entries for now then flush-out them later.
+                     * entries into local and shared database stats. Treat them
+                     * separately later.
                      */
-                    dbentlist = lappend(dbentlist, lent);
                     break;
                 case PGSTAT_TYPE_TABLE:
                     if (flush_tabstat(lent, nowait))
@@ -1268,9 +1257,11 @@ pgstat_report_stat(bool force)
         }
 
         /* Step 2: flush out database stats */
-        foreach(lc, dbentlist)
+        pgstat_localhash_start_iterate(pgStatLocalHash, &i);
+        while ((lent = pgstat_localhash_iterate(pgStatLocalHash, &i)) != NULL)
         {
-            PgStatLocalHashEntry *lent = (PgStatLocalHashEntry *) lfirst(lc);
+            /* no other types of entry must be found here */
+            Assert(lent->key.type == PGSTAT_TYPE_DB);
 
             if (flush_dbstat(lent, nowait))
             {
@@ -1281,8 +1272,6 @@ pgstat_report_stat(bool force)
                 pgstat_localhash_delete(pgStatLocalHash, lent->key);
             }
         }
-        list_free(dbentlist);
-        dbentlist = NULL;
 
         if (remains <= 0)
         {
@@ -1507,7 +1496,7 @@ flush_dbstat(PgStatLocalHashEntry *ent, bool nowait)
 
     Assert(ent->key.type == PGSTAT_TYPE_DB);
 
-    localent = (PgStat_StatDBEntry *) &ent->body;
+    localent = (PgStat_StatDBEntry *) ent->body;
 
     /* find shared database stats entry corresponding to the local entry */
     sharedent = (PgStat_StatDBEntry *)
@@ -3215,11 +3204,8 @@ pgstat_fetch_stat_dbentry(Oid dbid)
     /* should be called from backends */
     Assert(IsUnderPostmaster);
 
-    /* the simple cache doesn't work properly for InvalidOid */
-    Assert(dbid != InvalidOid);
-
     /* Return cached result if it is valid. */
-    if (cached_dbent_key.databaseid == dbid)
+    if (dbid != 0 && cached_dbent_key.databaseid == dbid)
         return &cached_dbent;
 
     shent = (PgStat_StatDBEntry *)