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 6fa60185241099eee02c82a1397ecbd08e519880..36c11709ab3309d84f0b58d8b5a2755c2a8c2c6b 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 $
  *
  *-------------------------------------------------------------------------
  */
@@ -120,6 +120,11 @@ 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));
 
        /*