Mysql: What is the difference between "slow_query_log" vs "log_slow_queries"

Question

If there is not any difference, why having two server parameters to achieve one behavior?

Answer 1

From mysql documentation:

The --log-slow-queries option is deprecated and is removed (along with the log_slow_queries system variable) in MySQL 5.6. Instead, use the --slow_query_log option to enable the slow query log and the --slow_query_log_file=file_name option to set the slow query log file name.

See here: http://dev.mysql.com/doc/refman/5.5/en/server-options.html#option_mysqld_log-slow-queries

Answer 2

log_slow_queries was deprecated in MySQL 5.1.29 by slow-query-log. The MySQL 5.1 Reference Manual has more details.