This change includes optimization for a lock wait rules and a new behaviour for

a REPLACE command. 

innobase/lock/lock0lock.c

@@ -759,9 +759,9 @@ lock_rec_has_to_wait(
 			that this has a lock bit set on the same record as
 			in the new lock we are setting */
 	ibool lock_is_on_supremum)  /* in: TRUE if we are setting the lock
-                                       on the 'supremum' record of an index page: we know
-                                       then that the lock request is really for a 'gap' type
-                                       lock */
+			on the 'supremum' record of an index
+			page: we know then that the lock request
+			is really for a 'gap' type lock */
 {
 	ut_ad(trx && lock2);
 	ut_ad(lock_get_type(lock2) == LOCK_REC);
@@ -773,11 +773,11 @@ lock_rec_has_to_wait(
 		/* We have somewhat complex rules when gap type record locks
 		cause waits */
 
-	        if( lock_is_on_supremum && !(type_mode & LOCK_INSERT_INTENTION))
-                {
-		        /* Lock on the supremum record is really a 'gap' type lock
-                           and gap type lock do not need to wait if it
-                           is not LOCK_INSERT_INTENSION type lock */
+		if (( lock_is_on_supremum || (type_mode & LOCK_GAP))
+			&& !(type_mode & LOCK_INSERT_INTENTION)) {
+			/* Gap type locks without LOCK_INSERT_INTENTION flag
+			do not need to wait for anything. This is because different 
+			users can have conflicting lock types on gaps. */
 						  
 			return(FALSE);
 		}
@@ -842,9 +842,12 @@ lock_has_to_wait(
 		if (lock_get_type(lock1) == LOCK_REC) {
 			ut_ad(lock_get_type(lock2) == LOCK_REC);
 
+			/* If this lock request is for a supremum record
+			then the second bit on the lock bitmap is set */
 			
 			return(lock_rec_has_to_wait(lock1->trx,
-			       lock1->type_mode, lock2,(ibool)lock_rec_get_nth_bit(lock1,1)));
+						lock1->type_mode, lock2,
+						lock_rec_get_nth_bit(lock1,1)));
 		}
 
 		return(TRUE);
@@ -1433,7 +1436,8 @@ lock_rec_other_has_conflicting(
 	lock = lock_rec_get_first(rec);
 
 	while (lock) {
-		if (lock_rec_has_to_wait(trx, mode, lock, (ibool)page_rec_is_supremum(rec))) {
+		if (lock_rec_has_to_wait(trx, mode, lock,
+			page_rec_is_supremum(rec))) {
 
 			return(lock);
 		}

innobase/row/row0ins.c

@@ -1029,7 +1029,7 @@ records */
 static
 ulint
 row_ins_set_exclusive_rec_lock(
-/*========================*/
+/*============================*/
 				/* out: DB_SUCCESS or error code */
 	ulint		type, 	/* in: LOCK_ORDINARY, LOCK_GAP, or
 				LOCK_REC_NOT_GAP type lock */
@@ -1517,21 +1517,17 @@ row_ins_scan_sec_index_for_duplicate(
 				
 		/* Try to place a lock on the index record */
 
-                /* The manual defines the REPLACE semantics that it 
-                   is either an INSERT or DELETE(s) for duplicate key
-                   + INSERT. Therefore, we should take X-lock for
-                   duplicates.
-		*/
-
-		trx = thr_get_trx(thr);*/* Get Transaction */
-
-                /* Is the first word in MySQL query REPLACE ? */
-
-		ut_ad(trx)
+		trx = thr_get_trx(thr);      
+		ut_ad(trx);
 		dict_accept(*trx->mysql_query_str, "REPLACE", &success);
 
 		if (success) {
 
+			/* The manual defines the REPLACE semantics that it 
+			is either an INSERT or DELETE(s) for duplicate key
+			+ INSERT. Therefore, we should take X-lock for 
+			duplicates */
+			
 			err = row_ins_set_exclusive_rec_lock(
 						LOCK_ORDINARY,rec,index,thr);
 		} else {
@@ -1540,7 +1536,6 @@ row_ins_scan_sec_index_for_duplicate(
 						LOCK_ORDINARY, rec, index,thr);
 		}
 
-
 		if (err != DB_SUCCESS) {
 
 			break;
@@ -1640,19 +1635,15 @@ row_ins_duplicate_error_in_clust(
 			sure that in roll-forward we get the same duplicate
 			errors as in original execution */
 
-                        /* The manual defines the REPLACE semantics that it 
-                           is either an INSERT or DELETE(s) for duplicate key
-                           + INSERT. Therefore, we should take X-lock for
-                           duplicates.
-		        */
-
-                        
-                        /* Is the first word in MySQL query REPLACE ? */
-
 			dict_accept(*trx->mysql_query_str, "REPLACE", &success);
 
 			if (success) {
 
+				/* The manual defines the REPLACE semantics that it 
+				is either an INSERT or DELETE(s) for duplicate key
+				+ INSERT. Therefore, we should take X-lock for
+				duplicates */
+				
 				err = row_ins_set_exclusive_rec_lock(
 					LOCK_REC_NOT_GAP,rec,cursor->index,thr);
 			} else {