When a transaction is waiting for a resource, it will wait for the resource to become free, or stop waiting and return with the error

ERROR HY000: Lock wait timeout exceeded; try restarting transaction

The length of time a transaction will wait for a resource before “giving up” is determined by the value of the configuration parameter innodb_lock_wait_timeout. The default setting for this parameter is 50 seconds. The minimum setting is 1 second, and values above 100,000,000 disable the timeout, so a transaction will wait “forever”. Following a timeout, the SQL statement that was executing will be rolled back. (In MySQL 5.0.12 and earlier, the transaction rolled back.) The user application may try the statement again (usually after waiting for a while), or rollback the entire transaction and restart.

Before InnoDB storage engine 1.0.2, the only way to set this parameter was in the MySQL option file (my.cnf or my.ini), and changing it required shutting down and restarting the server. Beginning with the InnoDB storage engine 1.0.2, the configuration parameter innodb_lock_wait_timeout can be set at runtime with the SET GLOBAL or SET SESSION commands. Changing the GLOBAL setting requires the SUPER privilege and affects the operation of all clients that subsequently connect. Any client can change the SESSION setting for innodb_lock_wait_timeout, which affects only that client.