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The path to the MySQL server data directory. Relative paths are resolved with respect to the current directory. If you expect the server to be started automatically (that is, in contexts for which you cannot know the current directory in advance), it is best to specify the datadir  value as an absolute path. 

• debug 

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This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug  option given at server startup. The global and session values may be set at runtime. 

Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges” . 

Assigning a value that begins with +  or -  cause the value to added to or subtracted from the current value: 

mysql> SET debug = ’T’; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | T | +---------+ mysql> SET debug = ’+P’; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | P:T | +---------+ mysql> SET debug = ’-P’; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | T | +---------+ 

For more information, see Section 5.9.4, “The DBUG Package” . 

• debug_sync 

