Server System Variables This section provides a description of each system variable. For a system variable summary table, see Section 5.1.5, “Server System Variable Reference” . For more information about manipulation of system variables, see Section 5.1.9, “Using System Variables” . For additional system variable information, see these sections: Some of the following variable descriptions refer to “enabling”  or “disabling”  a variable. These variables can be enabled with the  SET  statement by setting them to  ON  or  1 , or disabled by setting them to  OFF  or  0 . Boolean variables can be set at startup to the values  ON ,  TRUE ,  OFF , and  FALSE  (not case-sensitive), as well as  1 and  0 . See Section 4.2.2.4, “Program Option Modifiers” . Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server adjusts a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server sets the value to 1024. Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified. Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is  /var/mysql/data . If a file-valued variable is given as a relative path name, it is located under  /var/mysql/data . If the value is an absolute path name, its location is as given by the path name. 762 • activate_all_roles_on_login Command-Line Format --activate-all-roles-on-login[={OFF| ON}] System Variable activate_all_roles_on_login Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Boolean Default Value OFF Note •For information on server system variables specific to replication, see Section 17.1.6, “Replication and Binary Logging Options and Variables” . •NDB Cluster System Variables, lists system variables which are specific to NDB Cluster. •Information on tuning system variables can be found in Section 5.1.1, “Configuring the Server” . •Section 15.14, “InnoDB Startup Options and System Variables” , lists  InnoDB  system variables. •Section 5.1.9.2, “Dynamic System Variables” , lists the variables that can be set at runtime. •Section 5.1.9, “Using System Variables” , discusses the syntax for setting and displaying system variable values.