This guide will get you up and running with how to identify the bottleneck queries using the excellent tool pt-query-digest. You will learn how to use and analyze the output returned by pt-query-digest. You will also learn some differences between slow query logging in various MySQL versions. Later on in the post I will also show you how to make use of the extra diagnostic data available with Percona Server.

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The pt-query-digest tool has a number of special cases that affect how it “fingerprints” queries when it groups similar queries together to produce an aggregated report over the group. One of these is a special rule for queries that appear to come from mysqldump, of the following form:

SELECT /*!40001 SQL_NO_CACHE */ * FROM `users`

All such queries will be fingerprinted together and presented in a single class of queries. I remember many instances where mysqldump queries crowded the report of the “most important” queries and just caused other queries to be excluded. Grouping them together made it obvious that mysqldump’s load on the server was a problem, but didn’t obliterate other interesting things we wanted to see in the report.

Further Reading:

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