Analysing MySQL Slow Query Logs

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Analysing slow queries is mandatory in the process of optimization of all project.

A raw analysis of the result file can be quickly difficult. A lot of data, multiple line for each query detected, etc. can forbidden a global vision of the situation, in consequence, the correction become long and hard.

Some tools are available to help to do a rational optimization.


The own tool of MySql ! It can aggregate queries, sort by multiple criteria (query time, lock time, etc.). You can found all documentation and description on MySql Website or typing the following command:

$ mysqldumpslow --help
Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]

Parse and summarize the MySQL slow query log. Options are

  --verbose    verbose
  --debug      debug
  --help       write this text to standard output

  -v           verbose
  -d           debug
  -s ORDER     what to sort by (al, at, ar, ae, c, l, r, e, t), 'at' is default
                al: average lock time
                ar: average rows sent
                at: average query time
                 c: count
                 l: lock time
                 r: rows sent
                 t: query time  
  -r           reverse the sort order (largest last instead of first)
  -t NUM       just show the top n queries
  -a           don't abstract all numbers to N and strings to 'S'
  -n NUM       abstract numbers with at least n digits within names
  -g PATTERN   grep: only consider stmts that include this string
  -h HOSTNAME  hostname of db server for *-slow.log filename (can be wildcard),
               default is '*', i.e. match all
  -i NAME      name of server instance (if using mysql.server startup script)
  -l           don't subtract lock time from total time

Percona’s MySQL Slow Query Log Analyser

Since 2006, an alternative to analyse log is available : Percona Toolkit. The results are similar with as main difference with MySql's tool, it also prints a real example of the query allowing a copy and paste to MySQL for execution with EXPLAIN.

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