Exporting the mysql.slow_log table into slow query log format

Using pt-query-digest is an excellent way to perform a SQL review. However, sometimes you don't have access to the slow_query_log_file. For example, when MySQL runs on Amazon RDS, the slow_query_log_file is unavailable (see the RDS FAQ).

Overcoming Slow Log Access Restrictions in Amazon RDS

To get around this, export the mysql.slow_log table. To export the data, run the following SQL command from an instance that has database access. The data is exported into a MySQL slow-log format, which pt-query-digest can analyze:

mysql -u user -p -h host.rds.amazonaws.com -D mysql -s -r -e "SELECT CONCAT( '# Time: ', DATE_FORMAT(start_time, '%y%m%d %H%i%s'), '\n', '# User@Host: ', user_host, '\n', '# Query_time: ', TIME_TO_SEC(query_time), ' Lock_time: ', TIME_TO_SEC(lock_time), ' Rows_sent: ', rows_sent, ' Rows_examined: ', rows_examined, '\n', sql_text, ';' ) FROM mysql.slow_log" > /tmp/mysql.slow_log.log 

Understanding the Export Command Options

The -s (--silent) option is used to suppress echoing of the query. The -r (--raw) option is used to disable character escaping, making \n into an actual newline; otherwise, it's echoed as '\n'.

Analyzing the Log with pt-query-digest

Once the export is complete, run pt-query-digest to do the analysis. A simple review command is:

pt-query-digest --limit 100% /tmp/mysql.slow_log.log > /tmp/query-digest.txt 

query-digest.txt is now ready for review.

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