Avoid scanning the relcache during AtEOSubXact_RelationCache when there

is nothing to do, which is most of the time.  This is another simple
improvement to cut subtransaction entry/exit overhead.

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 6fa6018..36c1170 100644 (file)
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.211 2004/09/16 16:58:35 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.212 2004/11/20 20:19:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -121,6 +121,11 @@ static long relcacheInvalsReceived = 0L;
 static List *initFileRelationIds = NIL;
 
 /*
+ * This flag lets us optimize away work in AtEOSubXact_RelationCache().
+ */
+static bool need_eosubxact_work = false;
+
+/*
  *             RelationBuildDescInfo exists so code can be shared
  *             between RelationIdGetRelation() and RelationSysNameGetRelation()
  */
@@ -2087,6 +2092,9 @@ AtEOXact_RelationCache(bool isCommit)
                        relation->rd_indexvalid = 0;
                }
        }
+
+       /* Once done with the transaction, we can reset need_eosubxact_work */
+       need_eosubxact_work = false;
 }
 
 /*
@@ -2103,6 +2111,21 @@ AtEOSubXact_RelationCache(bool isCommit, SubTransactionId mySubid,
        HASH_SEQ_STATUS status;
        RelIdCacheEnt *idhentry;
 
+       /*
+        * In the majority of subtransactions there is not anything for this
+        * routine to do, and since there are usually many entries in the
+        * relcache, uselessly scanning the cache represents a surprisingly
+        * large fraction of the subtransaction entry/exit overhead.  To avoid
+        * this, we keep a static flag that must be set whenever a condition
+        * is created that requires subtransaction-end work.  (Currently, this
+        * means either a relation is created in the current xact, or an index
+        * list is forced.)  For simplicity, the flag remains set till end of
+        * top-level transaction, even though we could clear it earlier in some
+        * cases.
+        */
+       if (!need_eosubxact_work)
+               return;
+
        hash_seq_init(&status, RelationIdCache);
 
        while ((idhentry = (RelIdCacheEnt *) hash_seq_search(&status)) != NULL)
@@ -2184,6 +2207,9 @@ RelationBuildLocalRelation(const char *relname,
        /* it's being created in this transaction */
        rel->rd_createSubid = GetCurrentSubTransactionId();
 
+       /* must flag that we have rels created in this transaction */
+       need_eosubxact_work = true;
+
        /* is it a temporary relation? */
        rel->rd_istemp = isTempNamespace(relnamespace);
 
@@ -2745,6 +2771,8 @@ RelationSetIndexList(Relation relation, List *indexIds)
        list_free(relation->rd_indexlist);
        relation->rd_indexlist = indexIds;
        relation->rd_indexvalid = 2;    /* mark list as forced */
+       /* must flag that we have a forced index list */
+       need_eosubxact_work = true;
 }
 
 /*
@@ -3172,6 +3200,7 @@ load_relcache_init_file(void)
                        rel->rd_refcnt = 0;
                rel->rd_indexvalid = 0;
                rel->rd_indexlist = NIL;
+               rel->rd_createSubid = InvalidSubTransactionId;
                MemSet(&rel->pgstat_info, 0, sizeof(rel->pgstat_info));
 
                /*