xxxxxSQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded; try restarting transaction
When deadlock detection is enabled (the default) and a deadlock does occur, InnoDB detects the condition and rolls back one of the transactions (the victim). If deadlock detection is disabled using the innodb_deadlock_detect configuration option, InnoDB relies on the innodb_lock_wait_timeout setting to roll back transactions in case of a deadlock.
When deadlock detection is enabled (the default), InnoDB automatically detects transaction deadlocks and rolls back a transaction or transactions to break the deadlock.
When deadlock detection is enabled (the default), InnoDB automatically detects transaction deadlocks and rolls back a transaction or transactions to break the deadlock. InnoDB tries to pick small transactions to roll back, where the size of a transaction is determined by the number of rows inserted, updated, or deleted.
InnoDB is aware of table locks if innodb_table_locks = 1 (the default) and autocommit = 0, and the MySQL layer above it knows about row-level locks. Otherwise, InnoDB cannot detect deadlocks where a table lock set by a MySQL LOCK TABLES statement or a lock set by a storage engine other than InnoDB is involved. Resolve these situations by setting the value of theinnodb_lock_wait_timeout system variable.
On high concurrency systems, deadlock detection can cause a slowdown when numerous threads wait for the same lock. At times, it may be more efficient to disable deadlock detection and rely on the innodb_lock_wait_timeout setting for transaction rollback when a deadlock occurs. Deadlock detection can be disabled using the innodb_deadlock_detect configuration option.
The possibility of deadlocks is not affected by the isolation level, because the isolation level changes the behavior of read operations, while deadlocks occur because of write operations.