How to set up slow query logging for debugging of mysql configuration issues

Problem

flex.bi server gets very slow response times to import or report queries. Sometimes this is visible as timeout of reports, sometimes as error messages about not being able to lock records or other database related messages in queues log file.

Solution

Enabling logging of slow queries might help to trace the cause of the problem if it is database configuration problem. Enter these commands in you mysql configuration (usually /etc/my.cnf file):

long_query_time                = 10
slow_query_log                 = 1
slow_query_log_file            = /var/log/mysql/log-slow-queries.log

The create the file /var/log/mysql/log-slow-queries.log and make sure it can be accessed by the system user running mysql - usually user mysql. For example:

# mkdir /var/log/mysql
# touch /var/log/mysql/log-slow-queries.log
# chown mysql:mysql /var/log/mysql/log-slow-queries.log

Then restart mysql service and monitor the file.

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