Re: MySQL server configuration for a 8 cpu+20gb RAM server

[Rick James]

To record the slow queries as you go...
long_query_time = 2
log_slow_queries
--log-slow-queries

http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_long_query_time
http://dev.mysql.com/doc/refman/5.1/en/slow-query-log.html
http://dev.mysql.com/doc/refman/5.1/en/mysqldumpslow.html

I prefer having the data written to a file instead of a table.

If you switch entirely to InnoDB, shrink key_buffer_size to, say, 50M and increase innodb_buffer_pool_size to 70% of available RAM.