- Bug #16479309: FUNCTION LOCK_NUMBER_OF_ROWS_LOCKED MAY BE INEFFICIENT

  Locks held by a transaction are tracked using a bit-vector.
  For reporting, bit-vector is traversed to calculate number of locks held.
  This could be optimized by using a simple counter for tracking

  Approved: Sunny (rb#6478)

Author: Krunal Bauskar krunal.bauskar@oracle.com

storage/innobase/include/lock0priv.ic

@@ -96,6 +96,8 @@ lock_rec_set_nth_bit(
 	bit_index = i % 8;
 
 	((byte*) &lock[1])[byte_index] |= 1 << bit_index;
+
+	++lock->trx->lock.n_rec_locks;
 }
 
 /*********************************************************************//**

storage/innobase/include/trx0trx.h

@@ -774,6 +774,7 @@ struct trx_lock_t {
 					mutex to prevent recursive deadlocks.
 					Protected by both the lock sys mutex
 					and the trx_t::mutex. */
+	ulint		n_rec_locks;	/*!< number of rec locks in this trx */
 };
 
 #define TRX_MAGIC_N	91118598

storage/innobase/lock/lock0lock.cc

@@ -963,6 +963,12 @@ lock_rec_reset_nth_bit(
 	byte	mask = 1 << (i & 7);
 	byte	bit = *b & mask;
 	*b &= ~mask;
+
+	if (bit != 0) {
+		ut_ad(lock->trx->lock.n_rec_locks > 0);
+		--lock->trx->lock.n_rec_locks;
+	}
+
 	return(bit);
 }
 
@@ -1339,28 +1345,9 @@ lock_number_of_rows_locked(
 /*=======================*/
 	const trx_lock_t*	trx_lock)	/*!< in: transaction locks */
 {
-	const lock_t*	lock;
-	ulint		n_records = 0;
-
 	ut_ad(lock_mutex_own());
 
-	for (lock = UT_LIST_GET_FIRST(trx_lock->trx_locks);
-	     lock != NULL;
-	     lock = UT_LIST_GET_NEXT(trx_locks, lock)) {
-
-		if (lock_get_type_low(lock) == LOCK_REC) {
-			ulint	n_bit;
-			ulint	n_bits = lock_rec_get_n_bits(lock);
-
-			for (n_bit = 0; n_bit < n_bits; n_bit++) {
-				if (lock_rec_get_nth_bit(lock, n_bit)) {
-					n_records++;
-				}
-			}
-		}
-	}
-
-	return(n_records);
+	return(trx_lock->n_rec_locks);
 }
 
 /*********************************************************************//**
@@ -6386,6 +6373,8 @@ lock_trx_release_locks(
 
 	lock_release(trx);
 
+	trx->lock.n_rec_locks = 0;
+
 	lock_mutex_exit();
 
 	/* We don't remove the locks one by one from the vector for

storage/innobase/trx/trx0trx.cc

@@ -118,6 +118,8 @@ trx_init(
 
 	trx->support_xa = true;
 
+	trx->lock.n_rec_locks = 0;
+
 	trx->search_latch_timeout = BTR_SEA_TIMEOUT;
 
 	trx->dict_operation = TRX_DICT_OP_NONE;