Special mysqldump fingerprinting rule in pt-query-digest

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:

• New in mk-query-digest: variance-to-mean ratio
• Learn about mk-query-digest at PgEast 2010
• What’s new in mk-query-digest: EXPLAIN sparklines
• Slides from my session on mk-query-digest at PgEast 2010
• mk-query-digest now understands HTTP