*** pgsql/src/backend/utils/cache/relcache.c	2008/04/01 00:48:33	1.270
--- pgsql/src/backend/utils/cache/relcache.c	2008/04/16 18:23:04	1.271
***************
*** 8,14 ****
   *
   *
   * IDENTIFICATION
!  *	  $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.269 2008/03/26 21:10:39 alvherre Exp $
   *
   *-------------------------------------------------------------------------
   */
--- 8,14 ----
   *
   *
   * IDENTIFICATION
!  *	  $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.270 2008/04/01 00:48:33 tgl Exp $
   *
   *-------------------------------------------------------------------------
   */
*************** static OpClassCacheEnt *LookupOpclassInf
*** 220,227 ****
  /*
   *		ScanPgRelation
   *
!  *		this is used by RelationBuildDesc to find a pg_class
!  *		tuple matching targetRelId.
   *
   *		NB: the returned tuple has been copied into palloc'd storage
   *		and must eventually be freed with heap_freetuple.
--- 220,230 ----
  /*
   *		ScanPgRelation
   *
!  *		This is used by RelationBuildDesc to find a pg_class
!  *		tuple matching targetRelId.  The caller must hold at least
!  *		AccessShareLock on the target relid to prevent concurrent-update
!  *		scenarios --- else our SnapshotNow scan might fail to find any
!  *		version that it thinks is live.
   *
   *		NB: the returned tuple has been copied into palloc'd storage
   *		and must eventually be freed with heap_freetuple.
*************** equalRuleLocks(RuleLock *rlock1, RuleLoc
*** 773,790 ****
  }
  
  
! /* ----------------------------------
   *		RelationBuildDesc
   *
   *		Build a relation descriptor --- either a new one, or by
   *		recycling the given old relation object.  The latter case
   *		supports rebuilding a relcache entry without invalidating
!  *		pointers to it.
   *
   *		Returns NULL if no pg_class row could be found for the given relid
   *		(suggesting we are trying to access a just-deleted relation).
   *		Any other error is reported via elog.
-  * --------------------------------
   */
  static Relation
  RelationBuildDesc(Oid targetRelId, Relation oldrelation)
--- 776,793 ----
  }
  
  
! /*
   *		RelationBuildDesc
   *
   *		Build a relation descriptor --- either a new one, or by
   *		recycling the given old relation object.  The latter case
   *		supports rebuilding a relcache entry without invalidating
!  *		pointers to it.  The caller must hold at least
!  *		AccessShareLock on the target relid.
   *
   *		Returns NULL if no pg_class row could be found for the given relid
   *		(suggesting we are trying to access a just-deleted relation).
   *		Any other error is reported via elog.
   */
  static Relation
  RelationBuildDesc(Oid targetRelId, Relation oldrelation)
*************** RelationClose(Relation relation)
*** 1608,1613 ****
--- 1611,1620 ----
   *	RelationClearRelation just marks the entry as invalid by setting
   *	rd_isvalid to false.  This routine is called to fix the entry when it
   *	is next needed.
+  *
+  *	We assume that at the time we are called, we have at least AccessShareLock
+  *	on the target index.  (Note: in the calls from RelationClearRelation,
+  *	this is legitimate because we know the rel has positive refcount.)
   */
  static void
  RelationReloadIndexInfo(Relation relation)
*************** RelationReloadIndexInfo(Relation relatio
*** 1692,1697 ****
--- 1699,1707 ----
   *	 usually used when we are notified of a change to an open relation
   *	 (one with refcount > 0).  However, this routine just does whichever
   *	 it's told to do; callers must determine which they want.
+  *
+  *	 NB: when rebuilding, we'd better hold some lock on the relation.
+  *	 In current usages this is presumed true because it has refcnt > 0.
   */
  static void
  RelationClearRelation(Relation relation, bool rebuild)
*************** RelationCacheInitializePhase2(void)
*** 2542,2553 ****
--- 2552,2565 ----
  
  #define LOAD_CRIT_INDEX(indexoid) \
  		do { \
+ 			LockRelationOid(indexoid, AccessShareLock); \
  			ird = RelationBuildDesc(indexoid, NULL); \
  			if (ird == NULL) \
  				elog(PANIC, "could not open critical system index %u", \
  					 indexoid); \
  			ird->rd_isnailed = true; \
  			ird->rd_refcnt = 1; \
+ 			UnlockRelationOid(indexoid, AccessShareLock); \
  		} while (0)
  
  		LOAD_CRIT_INDEX(ClassOidIndexId);