MySQL性能优化 - 慢查询日志

1. 慢查询日志概述

• 说明

该日志记录执行时间超过阈值的SQL语句
注意:慢查询日志并不仅仅只记录select，update这种数据修改的SQL语句执行过长也会被记录

• 参数配置

慢SQL日志是Mysq(服务器提供的功能。在提供关键性监控数据的同时，还能够保持比较低的性能开销。
建议开启!

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2. 日志内容分析

日志分析辅助工具:mysqldumpslow、pt-query-digest

• mysqldumpslow
  指令使用帮助文档

[root@192 src]# 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, c, l, r, 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

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3. 生产环境中如何发现慢SQL

如加入ELK 等

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