Fix per-relation memory leakage in autovacuum.

PgStat_StatTabEntry and AutoVacOpts structs were leaked until
the end of the autovacuum worker's run, which is bad news if
there are a lot of relations in the database.

Note: pfree'ing the PgStat_StatTabEntry structs here seems a bit
risky, because pgstat_fetch_stat_tabentry_ext does not guarantee
anything about whether its result is long-lived.  It appears okay
so long as autovacuum forces PGSTAT_FETCH_CONSISTENCY_NONE, but
I think that API could use a re-think.

Also ensure that the VacuumRelation structure passed to
vacuum() is in recoverable storage.

Back-patch to v15 where we started to manage table statistics
this way.  (The AutoVacOpts leakage is probably older, but
I'm not excited enough to worry about just that part.)

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/285483.1746756246@sss.pgh.pa.us
Backpatch-through: 15

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 7b1de98d40425f7bb5ceef554747693f967d6070..4a5df4888600bdafba120b8ad528baf3e820bdab 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2211,6 +2211,12 @@ do_autovacuum(void)
                                }
                        }
                }
+
+               /* Release stuff to avoid per-relation leakage */
+               if (relopts)
+                       pfree(relopts);
+               if (tabentry)
+                       pfree(tabentry);
        }
 
        table_endscan(relScan);
@@ -2227,7 +2233,8 @@ do_autovacuum(void)
                Form_pg_class classForm = (Form_pg_class) GETSTRUCT(tuple);
                PgStat_StatTabEntry *tabentry;
                Oid                     relid;
-               AutoVacOpts *relopts = NULL;
+               AutoVacOpts *relopts;
+               bool            free_relopts = false;
                bool            dovacuum;
                bool            doanalyze;
                bool            wraparound;
@@ -2245,7 +2252,9 @@ do_autovacuum(void)
                 * main rel
                 */
                relopts = extract_autovac_opts(tuple, pg_class_desc);
-               if (relopts == NULL)
+               if (relopts)
+                       free_relopts = true;
+               else
                {
                        av_relation *hentry;
                        bool            found;
@@ -2266,6 +2275,12 @@ do_autovacuum(void)
                /* ignore analyze for toast tables */
                if (dovacuum)
                        table_oids = lappend_oid(table_oids, relid);
+
+               /* Release stuff to avoid leakage */
+               if (free_relopts)
+                       pfree(relopts);
+               if (tabentry)
+                       pfree(tabentry);
        }
 
        table_endscan(relScan);
@@ -2637,6 +2652,8 @@ deleted:
                pg_atomic_test_set_flag(&MyWorkerInfo->wi_dobalance);
        }
 
+       list_free(table_oids);
+
        /*
         * Perform additional work items, as requested by backends.
         */
@@ -2818,8 +2835,8 @@ deleted2:
 /*
  * extract_autovac_opts
  *
- * Given a relation's pg_class tuple, return the AutoVacOpts portion of
- * reloptions, if set; otherwise, return NULL.
+ * Given a relation's pg_class tuple, return a palloc'd copy of the
+ * AutoVacOpts portion of reloptions, if set; otherwise, return NULL.
  *
  * Note: callers do not have a relation lock on the table at this point,
  * so the table could have been dropped, and its catalog rows gone, after
@@ -2868,6 +2885,7 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
        autovac_table *tab = NULL;
        bool            wraparound;
        AutoVacOpts *avopts;
+       bool            free_avopts = false;
 
        /* fetch the relation's relcache entry */
        classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
@@ -2880,8 +2898,10 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
         * main table reloptions if the toast table itself doesn't have.
         */
        avopts = extract_autovac_opts(classTup, pg_class_desc);
-       if (classForm->relkind == RELKIND_TOASTVALUE &&
-               avopts == NULL && table_toast_map != NULL)
+       if (avopts)
+               free_avopts = true;
+       else if (classForm->relkind == RELKIND_TOASTVALUE &&
+                        table_toast_map != NULL)
        {
                av_relation *hentry;
                bool            found;
@@ -2983,6 +3003,8 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
                                                 avopts->vacuum_cost_delay >= 0));
        }
 
+       if (free_avopts)
+               pfree(avopts);
        heap_freetuple(classTup);
        return tab;
 }
@@ -3014,6 +3036,10 @@ recheck_relation_needs_vacanalyze(Oid relid,
                                                          effective_multixact_freeze_max_age,
                                                          dovacuum, doanalyze, wraparound);
 
+       /* Release tabentry to avoid leakage */
+       if (tabentry)
+               pfree(tabentry);
+
        /* ignore ANALYZE for toast tables */
        if (classForm->relkind == RELKIND_TOASTVALUE)
                *doanalyze = false;
@@ -3236,18 +3262,22 @@ autovacuum_do_vac_analyze(autovac_table *tab, BufferAccessStrategy bstrategy)
        VacuumRelation *rel;
        List       *rel_list;
        MemoryContext vac_context;
+       MemoryContext old_context;
 
        /* Let pgstat know what we're doing */
        autovac_report_activity(tab);
 
+       /* Create a context that vacuum() can use as cross-transaction storage */
+       vac_context = AllocSetContextCreate(CurrentMemoryContext,
+                                                                               "Vacuum",
+                                                                               ALLOCSET_DEFAULT_SIZES);
+
        /* Set up one VacuumRelation target, identified by OID, for vacuum() */
+       old_context = MemoryContextSwitchTo(vac_context);
        rangevar = makeRangeVar(tab->at_nspname, tab->at_relname, -1);
        rel = makeVacuumRelation(rangevar, tab->at_relid, NIL);
        rel_list = list_make1(rel);
-
-       vac_context = AllocSetContextCreate(CurrentMemoryContext,
-                                                                               "Vacuum",
-                                                                               ALLOCSET_DEFAULT_SIZES);
+       MemoryContextSwitchTo(old_context);
 
        vacuum(rel_list, &tab->at_params, bstrategy, vac_context, true);