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This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000. 

This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES , FLUSH TABLES WITH READ LOCK , and HANDLER  statements. 

This timeout does not apply to implicit accesses to system tables in the mysql  database, such as grant tables modified by GRANT  or REVOKE  statements or table logging statements. The timeout does apply to system tables accessed directly, such as with SELECT  or UPDATE . 

The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the lock_wait_timeout value before reporting a timeout error. When lock timeout occurs, ER_LOCK_WAIT_TIMEOUT  is reported. 

lock_wait_timeout  also defines the amount of time that a LOCK INSTANCE FOR BACKUP statement waits for a lock before giving up. 

• locked_in_memory 

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Whether mysqld  was locked in memory with --memlock . 

• log_error 

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The default error log destination. If the destination is the console, the value is stderr . Otherwise, the destination is a file and the log_error  value is the file name. See Section 5.4.2, “The Error Log” . 

