From 3e3f283e31b4e1da061970e048efe239a70b294d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 20 Nov 2004 20:19:52 +0000
Subject: [PATCH] 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.

---
 src/backend/utils/cache/relcache.c | 31 +++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 6fa6018524..36c11709ab 100644
--- 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));
 
 		/*
-- 
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