Merge heikki@bk-internal.mysql.com:/home/bk/mysql-5.0

into hundin.mysql.fi:/home/heikki/mysql-5.0

innobase/include/row0mysql.h

@@ -243,17 +243,27 @@ row_update_for_mysql(
 					the MySQL format */
 	row_prebuilt_t*	prebuilt);	/* in: prebuilt struct in MySQL
 					handle */
-
 /*************************************************************************
-Does an unlock of a row for MySQL. */
+This can only be used when srv_locks_unsafe_for_binlog is TRUE. Before
+calling this function we must use trx_reset_new_rec_lock_info() and
+trx_register_new_rec_lock() to store the information which new record locks
+really were set. This function removes a newly set lock under prebuilt->pcur,
+and also under prebuilt->clust_pcur. Currently, this is only used and tested
+in the case of an UPDATE or a DELETE statement, where the row lock is of the
+LOCK_X type.
+Thus, this implements a 'mini-rollback' that releases the latest record
+locks we set. */
 
 int
 row_unlock_for_mysql(
 /*=================*/
 					/* out: error code or DB_SUCCESS */
-	row_prebuilt_t*	prebuilt);	/* in: prebuilt struct in MySQL
+	row_prebuilt_t*	prebuilt,	/* in: prebuilt struct in MySQL
 					handle */
-
+	ibool		has_latches_on_recs);/* TRUE if called so that we have
+					the latches on the records under pcur
+					and clust_pcur, and we do not need to
+					reposition the cursors. */
 /*************************************************************************
 Creates an query graph node of 'update' type to be used in the MySQL
 interface. */

innobase/include/trx0trx.h

@@ -16,10 +16,39 @@ Created 3/26/1996 Heikki Tuuri
 #include "que0types.h"
 #include "mem0mem.h"
 #include "read0types.h"
+#include "dict0types.h"
 #include "trx0xa.h"
 
 extern ulint	trx_n_mysql_transactions;
 
+/*****************************************************************
+Resets the new record lock info in a transaction struct. */
+UNIV_INLINE
+void
+trx_reset_new_rec_lock_info(
+/*========================*/
+	trx_t*	trx);	/* in: transaction struct */
+/*****************************************************************
+Registers that we have set a new record lock on an index. We only have space
+to store 2 indexes! If this is called to store more than 2 indexes after
+trx_reset_new_rec_lock_info(), then this function does nothing. */
+UNIV_INLINE
+void
+trx_register_new_rec_lock(
+/*======================*/
+	trx_t*		trx,	/* in: transaction struct */
+	dict_index_t*	index);	/* in: trx sets a new record lock on this
+				index */
+/*****************************************************************
+Checks if trx has set a new record lock on an index. */
+UNIV_INLINE
+ibool
+trx_new_rec_locks_contain(
+/*======================*/
+				/* out: TRUE if trx has set a new record lock
+				on index */
+	trx_t*		trx,	/* in: transaction struct */
+	dict_index_t*	index);	/* in: index */
 /************************************************************************
 Releases the search latch if trx has reserved it. */
 
@@ -495,8 +524,18 @@ struct trx_struct{
 	lock_t*		auto_inc_lock;	/* possible auto-inc lock reserved by
 					the transaction; note that it is also
 					in the lock list trx_locks */
-	ibool		trx_create_lock;/* this is TRUE if we have created a
-					new lock for a record accessed */
+	dict_index_t*	new_rec_locks[2];/* these are normally NULL; if
+					srv_locks_unsafe_for_binlog is TRUE,
+					in a cursor search, if we set a new
+					record lock on an index, this is set
+					to point to the index; this is
+					used in releasing the locks under the
+					cursors if we are performing an UPDATE
+					and we determine after retrieving
+					the row that it does not need to be
+					locked; thus, these can be used to
+					implement a 'mini-rollback' that
+					releases the latest record locks */
 	UT_LIST_NODE_T(trx_t)
 			trx_list;	/* list of transactions */
 	UT_LIST_NODE_T(trx_t)

innobase/include/trx0trx.ic

@@ -39,4 +39,60 @@ trx_start_if_not_started_low(
 	}
 }
 
+/*****************************************************************
+Resets the new record lock info in a transaction struct. */
+UNIV_INLINE
+void
+trx_reset_new_rec_lock_info(
+/*========================*/
+	trx_t*	trx)	/* in: transaction struct */
+{
+	trx->new_rec_locks[0] = NULL;
+	trx->new_rec_locks[1] = NULL;
+}
+
+/*****************************************************************
+Registers that we have set a new record lock on an index. We only have space
+to store 2 indexes! If this is called to store more than 2 indexes after
+trx_reset_new_rec_lock_info(), then this function does nothing. */
+UNIV_INLINE
+void
+trx_register_new_rec_lock(
+/*======================*/
+	trx_t*		trx,	/* in: transaction struct */
+	dict_index_t*	index)	/* in: trx sets a new record lock on this
+				index */
+{
+	if (trx->new_rec_locks[0] == NULL) {
+		trx->new_rec_locks[0] = index;
+
+		return;
+	}
+
+	if (trx->new_rec_locks[0] == index) {
 
+		return;
+	}
+
+	if (trx->new_rec_locks[1] != NULL) {
+
+		return;
+	}
+
+	trx->new_rec_locks[1] = index;
+}
+
+/*****************************************************************
+Checks if trx has set a new record lock on an index. */
+UNIV_INLINE
+ibool
+trx_new_rec_locks_contain(
+/*======================*/
+				/* out: TRUE if trx has set a new record lock
+				on index */
+	trx_t*		trx,	/* in: transaction struct */
+	dict_index_t*	index)	/* in: index */
+{
+	return(trx->new_rec_locks[0] == index
+	       || trx->new_rec_locks[1] == index);
+}

innobase/lock/lock0lock.c

@@ -956,7 +956,7 @@ lock_rec_has_to_wait(
 		cause waits */
 
 		if ((lock_is_on_supremum || (type_mode & LOCK_GAP))
-			&& !(type_mode & LOCK_INSERT_INTENTION)) {
+		    && !(type_mode & LOCK_INSERT_INTENTION)) {
 
 			/* Gap type locks without LOCK_INSERT_INTENTION flag
 			do not need to wait for anything. This is because 
@@ -1765,10 +1765,7 @@ lock_rec_create(
 	lock_rec_set_nth_bit(lock, heap_no);
 
 	HASH_INSERT(lock_t, hash, lock_sys->rec_hash,
-					lock_rec_fold(space, page_no), lock); 
-	/* Note that we have create a new lock */
-	trx->trx_create_lock = TRUE;
-
+					lock_rec_fold(space, page_no), lock);
 	if (type_mode & LOCK_WAIT) {
 
 		lock_set_lock_and_trx_wait(lock, trx);
@@ -1945,15 +1942,6 @@ lock_rec_add_to_queue(
 
 	if (similar_lock && !somebody_waits && !(type_mode & LOCK_WAIT)) {
 
-		/* If the nth bit of a record lock is already set then we
-		do not set a new lock bit, otherwice we set */
-
-		if (lock_rec_get_nth_bit(similar_lock, heap_no)) {
-			trx->trx_create_lock = FALSE;
-		} else {
-			trx->trx_create_lock = TRUE;
-		}
-
 		lock_rec_set_nth_bit(similar_lock, heap_no);
 
 		return(similar_lock);
@@ -2005,11 +1993,14 @@ lock_rec_lock_fast(
 	lock = lock_rec_get_first_on_page(rec);
 
 	trx = thr_get_trx(thr);
-	trx->trx_create_lock = FALSE;
 
 	if (lock == NULL) {
 		if (!impl) {
 			lock_rec_create(mode, rec, index, trx);
+			
+			if (srv_locks_unsafe_for_binlog) {
+				trx_register_new_rec_lock(trx, index);
+			}
 		}
 		
 		return(TRUE);
@@ -2021,23 +2012,22 @@ lock_rec_lock_fast(
 	}
 
 	if (lock->trx != trx
-				|| lock->type_mode != (mode | LOCK_REC)
-				|| lock_rec_get_n_bits(lock) <= heap_no) {
+	    || lock->type_mode != (mode | LOCK_REC)
+	    || lock_rec_get_n_bits(lock) <= heap_no) {
+
 	    	return(FALSE);
 	}
 
 	if (!impl) {
+		/* If the nth bit of the record lock is already set then we
+		do not set a new lock bit, otherwise we do set */
 
-		/* If the nth bit of a record lock is already set then we
-		do not set a new lock bit, otherwice we set */
-
-		if (lock_rec_get_nth_bit(lock, heap_no)) {
-			trx->trx_create_lock = FALSE;
-		} else {
-			trx->trx_create_lock = TRUE;
+		if (!lock_rec_get_nth_bit(lock, heap_no)) {
+			lock_rec_set_nth_bit(lock, heap_no);
+			if (srv_locks_unsafe_for_binlog) {
+				trx_register_new_rec_lock(trx, index);
+			}
 		}
-
-		lock_rec_set_nth_bit(lock, heap_no);
 	}
 
 	return(TRUE);
@@ -2093,12 +2083,19 @@ lock_rec_lock_slow(
 		enough already granted on the record, we have to wait. */
     				
 		err = lock_rec_enqueue_waiting(mode, rec, index, thr);
+
+		if (srv_locks_unsafe_for_binlog) {
+			trx_register_new_rec_lock(trx, index);
+		}
 	} else {
 		if (!impl) {
 			/* Set the requested lock on the record */
 
 			lock_rec_add_to_queue(LOCK_REC | mode, rec, index,
 									trx);
+			if (srv_locks_unsafe_for_binlog) {
+				trx_register_new_rec_lock(trx, index);
+			}
 		}
 
 		err = DB_SUCCESS;
@@ -2436,8 +2433,15 @@ lock_rec_inherit_to_gap(
 	
 	lock = lock_rec_get_first(rec);
 
+	/* If srv_locks_unsafe_for_binlog is TRUE, we do not want locks set
+	by an UPDATE or a DELETE to be inherited as gap type locks. But we
+	DO want S-locks set by a consistency constraint to be inherited also
+	then. */
+
 	while (lock != NULL) {
-		if (!lock_rec_get_insert_intention(lock)) {
+		if (!lock_rec_get_insert_intention(lock)
+		    && !(srv_locks_unsafe_for_binlog
+			 && lock_get_mode(lock) == LOCK_X)) {
 			
 			lock_rec_add_to_queue(LOCK_REC | lock_get_mode(lock)
 						| LOCK_GAP,
@@ -3069,7 +3073,7 @@ lock_update_insert(
 	lock_rec_inherit_to_gap_if_gap_lock(rec, page_rec_get_next(rec));
 
 	lock_mutex_exit_kernel();
-}	
+}
 
 /*****************************************************************
 Updates the lock table when a record is removed. */

innobase/row/row0mysql.c

@@ -1429,51 +1429,106 @@ run_again:
 }
 
 /*************************************************************************
-Does an unlock of a row for MySQL. */
+This can only be used when srv_locks_unsafe_for_binlog is TRUE. Before
+calling this function we must use trx_reset_new_rec_lock_info() and
+trx_register_new_rec_lock() to store the information which new record locks
+really were set. This function removes a newly set lock under prebuilt->pcur,
+and also under prebuilt->clust_pcur. Currently, this is only used and tested
+in the case of an UPDATE or a DELETE statement, where the row lock is of the
+LOCK_X type.
+Thus, this implements a 'mini-rollback' that releases the latest record
+locks we set. */
 
 int
 row_unlock_for_mysql(
 /*=================*/
 					/* out: error code or DB_SUCCESS */
-	row_prebuilt_t*	prebuilt)	/* in: prebuilt struct in MySQL
+	row_prebuilt_t*	prebuilt,	/* in: prebuilt struct in MySQL
 					handle */
+	ibool		has_latches_on_recs)/* TRUE if called so that we have
+					the latches on the records under pcur
+					and clust_pcur, and we do not need to
+					reposition the cursors. */
 {
-	rec_t*		rec;
-	btr_pcur_t*	cur		= prebuilt->pcur;
+	dict_index_t*	index;
+	btr_pcur_t*	pcur		= prebuilt->pcur;
+	btr_pcur_t*	clust_pcur	= prebuilt->clust_pcur;
 	trx_t*		trx		= prebuilt->trx;
+	rec_t*		rec;
 	mtr_t           mtr;
 	
 	ut_ad(prebuilt && trx);
 	ut_ad(trx->mysql_thread_id == os_thread_get_curr_id());
-		
+			
+	if (!srv_locks_unsafe_for_binlog) {
+
+		fprintf(stderr,
+"InnoDB: Error: calling row_unlock_for_mysql though\n"
+"InnoDB: srv_locks_unsafe_for_binlog is FALSE.\n");
+
+		return(DB_SUCCESS);
+	}
+
 	trx->op_info = "unlock_row";
-	
-	if (srv_locks_unsafe_for_binlog) {
-		if (trx->trx_create_lock == TRUE) {
 
-			mtr_start(&mtr);
+	index = btr_pcur_get_btr_cur(pcur)->index;
+
+	if (index != NULL && trx_new_rec_locks_contain(trx, index)) {
+
+		mtr_start(&mtr);
 			
-			/* Restore a cursor position and find a record */
-			btr_pcur_restore_position(BTR_SEARCH_LEAF, cur, &mtr);
-			rec = btr_pcur_get_rec(cur);
+		/* Restore the cursor position and find the record */
+		
+		if (!has_latches_on_recs) {
+			btr_pcur_restore_position(BTR_SEARCH_LEAF, pcur, &mtr);
+		}
 
-			if (rec) {
+		rec = btr_pcur_get_rec(pcur);
 
-				lock_rec_reset_and_release_wait(rec);
-			} else {
-				fputs("InnoDB: Error: "
-				      "Record for the lock not found\n",
-				      stderr);
-				mem_analyze_corruption((byte*) trx);
-				ut_error;
-			}
+		mutex_enter(&kernel_mutex);
 
-			trx->trx_create_lock = FALSE;
-			mtr_commit(&mtr);
+		lock_rec_reset_and_release_wait(rec);
+
+		mutex_exit(&kernel_mutex);
+
+		mtr_commit(&mtr);
+
+		/* If the search was done through the clustered index, then
+		we have not used clust_pcur at all, and we must NOT try to
+		reset locks on clust_pcur. The values in clust_pcur may be
+		garbage! */
+
+		if (index->type & DICT_CLUSTERED) {
+			
+			goto func_exit;
 		}
-		
+	}
+
+	index = btr_pcur_get_btr_cur(clust_pcur)->index;
+
+	if (index != NULL && trx_new_rec_locks_contain(trx, index)) {
+
+		mtr_start(&mtr);
+			
+		/* Restore the cursor position and find the record */
+
+		if (!has_latches_on_recs) {
+			btr_pcur_restore_position(BTR_SEARCH_LEAF, clust_pcur,
+									&mtr);
+		}
+
+		rec = btr_pcur_get_rec(clust_pcur);
+
+		mutex_enter(&kernel_mutex);
+
+		lock_rec_reset_and_release_wait(rec);
+
+		mutex_exit(&kernel_mutex);
+
+		mtr_commit(&mtr);
 	}
 			
+func_exit:
 	trx->op_info = "";
 	
 	return(DB_SUCCESS);

innobase/row/row0sel.c

@@ -2784,6 +2784,10 @@ sel_restore_position_for_mysql(
 					process the record the cursor is
 					now positioned on (i.e. we should
 					not go to the next record yet) */
+	ibool*		same_user_rec,	/* out: TRUE if we were able to restore
+					the cursor on a user record with the
+					same ordering prefix in in the
+					B-tree index */
 	ulint		latch_mode,	/* in: latch mode wished in
 					restoration */
 	btr_pcur_t*	pcur,		/* in: cursor whose position
@@ -2800,6 +2804,8 @@ sel_restore_position_for_mysql(
 	
 	success = btr_pcur_restore_position(latch_mode, pcur, mtr);
 
+	*same_user_rec = success;
+
 	if (relative_position == BTR_PCUR_ON) {
 		if (success) {
 			return(FALSE);
@@ -3064,10 +3070,12 @@ row_search_for_mysql(
 	ulint		cnt				= 0;
 #endif /* UNIV_SEARCH_DEBUG */
 	ulint		next_offs;
+	ibool		same_user_rec;
 	mtr_t		mtr;
 	mem_heap_t*	heap				= NULL;
 	ulint		offsets_[REC_OFFS_NORMAL_SIZE];
 	ulint*		offsets				= offsets_;
+
 	*offsets_ = (sizeof offsets_) / sizeof *offsets_;
 
 	ut_ad(index && pcur && search_tuple);
@@ -3138,6 +3146,14 @@ row_search_for_mysql(
 		trx->search_latch_timeout = BTR_SEA_TIMEOUT;
 	}
 	
+	/* Reset the new record lock info if we srv_locks_unsafe_for_binlog
+	is set. Then we are able to remove the record locks set here on an
+	individual row. */
+
+	if (srv_locks_unsafe_for_binlog) {
+		trx_reset_new_rec_lock_info(trx);
+	}
+
 	/*-------------------------------------------------------------*/
 	/* PHASE 1: Try to pop the row from the prefetch cache */
 
@@ -3396,8 +3412,9 @@ shortcut_fails_too_big_rec:
 	clust_index = dict_table_get_first_index(index->table);
 
 	if (UNIV_LIKELY(direction != 0)) {
-		if (!sel_restore_position_for_mysql(BTR_SEARCH_LEAF, pcur,
-							moves_up, &mtr)) {
+		if (!sel_restore_position_for_mysql(&same_user_rec,
+						BTR_SEARCH_LEAF,
+						pcur, moves_up, &mtr)) {
 			goto next_rec;
 		}
 
@@ -3659,7 +3676,7 @@ rec_loop:
 			goto normal_return;
 		}
 	}
-		
+
 	/* We are ready to look at a possible new index entry in the result
 	set: the cursor is now placed on a user record */
 
@@ -3679,6 +3696,7 @@ rec_loop:
 		    || srv_locks_unsafe_for_binlog
 		    || (unique_search && !UNIV_UNLIKELY(rec_get_deleted_flag(
 					rec, page_rec_is_comp(rec))))) {
+
 			goto no_gap_lock;
 		} else {
 			lock_type = LOCK_ORDINARY;
@@ -3701,7 +3719,7 @@ rec_loop:
 		    && dtuple_get_n_fields_cmp(search_tuple)
 		       == dict_index_get_n_unique(index)
 		    && 0 == cmp_dtuple_rec(search_tuple, rec, offsets)) {
-		no_gap_lock:
+no_gap_lock:
 			lock_type = LOCK_REC_NOT_GAP;
 		}
 
@@ -3764,6 +3782,7 @@ rec_loop:
 			/* Get the clustered index record if needed */
 			index_rec = rec;
 			ut_ad(index != clust_index);
+
 			goto requires_clust_rec;
 		}
 	}
@@ -3773,6 +3792,15 @@ rec_loop:
 		/* The record is delete-marked: we can skip it if this is
 		not a consistent read which might see an earlier version
 		of a non-clustered index record */
+
+		if (srv_locks_unsafe_for_binlog) {
+			/* No need to keep a lock on a delete-marked record
+			if we do not want to use next-key locking. */
+
+			row_unlock_for_mysql(prebuilt, TRUE);
+			
+			trx_reset_new_rec_lock_info(trx);
+		}
 		
 		goto next_rec;
 	}
@@ -3783,7 +3811,8 @@ rec_loop:
 	index_rec = rec;
 
 	if (index != clust_index && prebuilt->need_to_access_clustered) {
-	requires_clust_rec:
+
+requires_clust_rec:
 		/* Before and after this "if" block, "offsets" will be
 		related to "rec", which may be in a secondary index "index" or
 		the clustered index ("clust_index").  However, after this
@@ -3816,6 +3845,16 @@ rec_loop:
 
 			/* The record is delete marked: we can skip it */
 
+			if (srv_locks_unsafe_for_binlog) {
+				/* No need to keep a lock on a delete-marked
+				record if we do not want to use next-key
+				locking. */
+
+				row_unlock_for_mysql(prebuilt, TRUE);
+			
+				trx_reset_new_rec_lock_info(trx);
+			}
+
 			goto next_rec;
 		}
 		
@@ -3908,7 +3947,7 @@ got_row:
 next_rec:
 	/*-------------------------------------------------------------*/
 	/* PHASE 5: Move the cursor to the next index record */
-	
+
 	if (UNIV_UNLIKELY(mtr_has_extra_clust_latch)) {
 		/* We must commit mtr if we are moving to the next
 		non-clustered index record, because we could break the
@@ -3921,8 +3960,9 @@ next_rec:
 		mtr_has_extra_clust_latch = FALSE;
 	
 		mtr_start(&mtr);
-		if (sel_restore_position_for_mysql(BTR_SEARCH_LEAF, pcur,
-							moves_up, &mtr)) {
+		if (sel_restore_position_for_mysql(&same_user_rec,
+						BTR_SEARCH_LEAF,
+						pcur, moves_up, &mtr)) {
 #ifdef UNIV_SEARCH_DEBUG
 			cnt++;
 #endif /* UNIV_SEARCH_DEBUG */
@@ -3976,8 +4016,29 @@ lock_wait_or_error:
 		thr->lock_state = QUE_THR_LOCK_NOLOCK;
 		mtr_start(&mtr);
 
-		sel_restore_position_for_mysql(BTR_SEARCH_LEAF, pcur,
-							moves_up, &mtr);
+		sel_restore_position_for_mysql(&same_user_rec,
+						BTR_SEARCH_LEAF, pcur,
+						moves_up, &mtr);
+		if (srv_locks_unsafe_for_binlog && !same_user_rec) {
+			/* Since we were not able to restore the cursor
+			on the same user record, we cannot use
+			row_unlock_for_mysql() to unlock any records, and
+			we must thus reset the new rec lock info. Since
+			in lock0lock.c we have blocked the inheriting of gap
+			X-locks, we actually do not have any new record locks
+			set in this case.
+
+			Note that if we were able to restore on the 'same'
+			user record, it is still possible that we were actually
+			waiting on a delete-marked record, and meanwhile
+			it was removed by purge and inserted again by some
+			other user. But that is no problem, because in
+			rec_loop we will again try to set a lock, and
+			new_rec_lock_info in trx will be right at the end. */
+
+			trx_reset_new_rec_lock_info(trx);
+		}
+	
 		mode = pcur->search_mode;
 
 		goto rec_loop;

innobase/trx/trx0trx.c

@@ -166,6 +166,8 @@ trx_create(
 	memset(&trx->xid, 0, sizeof(trx->xid));
 	trx->xid.formatID = -1;
 
+	trx_reset_new_rec_lock_info(trx);
+
 	return(trx);
 }
 

sql/ha_innodb.cc

@@ -1496,8 +1496,8 @@ innobase_start_trx_and_assign_read_view(
 /*********************************************************************
 Commits a transaction in an InnoDB database or marks an SQL statement
 ended. */
-
-static int
+static
+int
 innobase_commit(
 /*============*/
 			/* out: 0 */
@@ -3538,7 +3538,9 @@ ha_innobase::delete_row(
 }
 
 /**************************************************************************
-Deletes a lock set to a row */
+Removes a new lock set on a row. This can be called after a row has been read
+in the processing of an UPDATE or a DELETE query, if the option
+innodb_locks_unsafe_for_binlog is set. */
 
 void
 ha_innobase::unlock_row(void)
@@ -3556,8 +3558,10 @@ ha_innobase::unlock_row(void)
 		mem_analyze_corruption((byte *) prebuilt->trx);
 		ut_error;
 	}
-
-	row_unlock_for_mysql(prebuilt);
+	
+	if (srv_locks_unsafe_for_binlog) {
+		row_unlock_for_mysql(prebuilt, FALSE);
+	}
 }
 
 /**********************************************************************
@@ -5991,6 +5995,7 @@ ha_innobase::external_lock(
 			reads. */
 
 			prebuilt->select_lock_type = LOCK_S;
+			prebuilt->stored_select_lock_type = LOCK_S;
 		}
 
 		/* Starting from 4.1.9, no InnoDB table lock is taken in LOCK
@@ -6030,7 +6035,6 @@ ha_innobase::external_lock(
 	trx->n_mysql_tables_in_use--;
 	prebuilt->mysql_has_locked = FALSE;
 
-
 	/* If the MySQL lock count drops to zero we know that the current SQL
 	statement has ended */
 
@@ -6563,12 +6567,14 @@ the value of the auto-inc counter. */
 int
 ha_innobase::innobase_read_and_init_auto_inc(
 /*=========================================*/
-				/* out: 0 or error code: deadlock or
-				lock wait timeout */
+				/* out: 0 or error code: deadlock or lock wait
+				timeout */
 	longlong*	ret)	/* out: auto-inc value */
 {
   	row_prebuilt_t* prebuilt	= (row_prebuilt_t*) innobase_prebuilt;
     	longlong        auto_inc;
+	ulint		old_select_lock_type;
+	ibool		trx_was_not_started	= FALSE;
   	int     	error;
 
   	ut_a(prebuilt);
@@ -6576,6 +6582,10 @@ ha_innobase::innobase_read_and_init_auto_inc(
                 (trx_t*) current_thd->ha_data[innobase_hton.slot]);
 	ut_a(prebuilt->table);
 	
+	if (prebuilt->trx->conc_state == TRX_NOT_STARTED) {
+		trx_was_not_started = TRUE;
+	}
+
 	/* In case MySQL calls this in the middle of a SELECT query, release
 	possible adaptive hash latch to avoid deadlocks of threads */
 
@@ -6587,7 +6597,9 @@ ha_innobase::innobase_read_and_init_auto_inc(
 		/* Already initialized */
 		*ret = auto_inc;
 	
-		return(0);
+		error = 0;
+
+		goto func_exit_early;
 	}
 
 	error = row_lock_table_autoinc_for_mysql(prebuilt);
@@ -6595,7 +6607,7 @@ ha_innobase::innobase_read_and_init_auto_inc(
 	if (error != DB_SUCCESS) {
 		error = convert_error_code_to_mysql(error, user_thd);
 
-		goto func_exit;
+		goto func_exit_early;
 	}	
 
 	/* Check again if someone has initialized the counter meanwhile */
@@ -6604,30 +6616,37 @@ ha_innobase::innobase_read_and_init_auto_inc(
 	if (auto_inc != 0) {
 		*ret = auto_inc;
 	
-		return(0);
+		error = 0;
+
+		goto func_exit_early;
 	}
 
   	(void) extra(HA_EXTRA_KEYREAD);
   	index_init(table->s->next_number_index);
 
-	/* We use an exclusive lock when we read the max key value from the
-  	auto-increment column index. This is because then build_template will
-  	advise InnoDB to fetch all columns. In SHOW TABLE STATUS the query
-  	id of the auto-increment column is not changed, and previously InnoDB
-  	did not fetch it, causing SHOW TABLE STATUS to show wrong values
-  	for the autoinc column. */
-
-  	prebuilt->select_lock_type = LOCK_X;
+	/* Starting from 5.0.9, we use a consistent read to read the auto-inc
+	column maximum value. This eliminates the spurious deadlocks caused
+	by the row X-lock that we previously used. Note the following flaw
+	in our algorithm: if some other user meanwhile UPDATEs the auto-inc
+	column, our consistent read will not return the largest value. We
+	accept this flaw, since the deadlocks were a bigger trouble. */
 
-  	/* Play safe and also give in another way the hint to fetch
-  	all columns in the key: */
+  	/* Fetch all the columns in the key */
   	
 	prebuilt->hint_need_to_fetch_extra_cols = ROW_RETRIEVE_ALL_COLS;
 
-	prebuilt->trx->mysql_n_tables_locked += 1;
-  
+	old_select_lock_type = prebuilt->select_lock_type;
+  	prebuilt->select_lock_type = LOCK_NONE;
+
+	/* Eliminate an InnoDB error print that happens when we try to SELECT
+	from a table when no table has been locked in ::external_lock(). */
+	prebuilt->trx->n_mysql_tables_in_use++;
+
 	error = index_last(table->record[1]);
 
+	prebuilt->trx->n_mysql_tables_in_use--;
+  	prebuilt->select_lock_type = old_select_lock_type;
+
   	if (error) {
 		if (error == HA_ERR_END_OF_FILE) {
 			/* The table was empty, initialize to 1 */
@@ -6635,7 +6654,10 @@ ha_innobase::innobase_read_and_init_auto_inc(
 
 			error = 0;
 		} else {
-			/* Deadlock or a lock wait timeout */
+			/* This should not happen in a consistent read */
+			fprintf(stderr,
+"InnoDB: Error: consistent read of auto-inc column returned %lu\n",
+								(ulong)error);
   			auto_inc = -1;
 
   			goto func_exit;
@@ -6655,7 +6677,18 @@ func_exit:
 
 	*ret = auto_inc;
 
-  	return(error);
+func_exit_early:
+	/* Since MySQL does not seem to call autocommit after SHOW TABLE
+	STATUS (even if we would register the trx here), we must commit our
+	transaction here if it was started here. This is to eliminate a
+	dangling transaction. */
+
+	if (trx_was_not_started) {
+
+		innobase_commit_low(prebuilt->trx);
+	}
+
+ 	return(error);
 }
 
 /***********************************************************************