SET GLOBAL mroonga_log_file = "groonga-query-log.log";
SET GLOBAL mroonga_query_log_file = NULL;
SHOW GLOBAL VARIABLES LIKE "mroonga_query_log_file";
Variable_name	Value
mroonga_query_log_file	
log file is changed: <groonga.log> -> <groonga-query-log.log>
query log file is still disabled
SET GLOBAL mroonga_query_log_file = DEFAULT;
SET GLOBAL mroonga_log_file = DEFAULT;
