Adjust GetLockConflicts() so that it uses TopMemoryContext when

executed InHotStandby. Cleaner solution than using malloc or palloc
depending upon situation, as proposed by Tom.

Author: simonat2ndQuadrant

src/backend/storage/lmgr/lock.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.192 2010/01/28 10:05:37 sriggs Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.193 2010/01/29 19:45:12 sriggs Exp $
  *
  * NOTES
  *	  A lock table is a shared memory hash table.  When
@@ -1790,7 +1790,7 @@ LockReassignCurrentOwner(void)
 VirtualTransactionId *
 GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode)
 {
-	static VirtualTransactionId *vxids = NULL;
+	static VirtualTransactionId *vxids;
 	LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid;
 	LockMethod	lockMethodTable;
 	LOCK	   *lock;
@@ -1810,24 +1810,18 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode)
 	/*
 	 * Allocate memory to store results, and fill with InvalidVXID.  We only
 	 * need enough space for MaxBackends + a terminator, since prepared xacts
-	 * don't count.
+	 * don't count. InHotStandby allocate once in TopMemoryContext.
 	 */
-	if (!InHotStandby)
-		vxids = (VirtualTransactionId *)
-			palloc0(sizeof(VirtualTransactionId) * (MaxBackends + 1));
-	else
+	if (InHotStandby)
 	{
 		if (vxids == NULL)
-		{
 			vxids = (VirtualTransactionId *)
-				malloc(sizeof(VirtualTransactionId) * (MaxBackends + 1));
-			if (vxids == NULL)
-				ereport(ERROR,
-					(errcode(ERRCODE_OUT_OF_MEMORY),
-					 errmsg("out of memory")));
-
-		}
+				MemoryContextAlloc(TopMemoryContext,
+					sizeof(VirtualTransactionId) * (MaxBackends + 1));
 	}
+	else
+		vxids = (VirtualTransactionId *)
+			palloc0(sizeof(VirtualTransactionId) * (MaxBackends + 1));
 
 	/*
 	 * Look up the lock object matching the tag.