MySQL慢查询日志的使用详解

使用慢查询日志里捕获

启用之前需要先进行一些设置

 

方法一：全局变量设置

 

设置慢查询日志的日志文件位置 set global slow_query_log_file = "D:/slow_log/slow_log.log" ;

 

设置是否对未使用索引的SQL进行记录 set global log_queries_not_using_indexes = on;

 

设置只要SQL执行时间超过n秒的就记录 set global long_query_time = 0.001 ;

此处设置的0.001秒，便于测试，一般情况比这个大

 

启用MySQL慢查询日志 set global slow_query_log = on;

 

方法二：配置文件设置

修改配置文件my.cnf，在[mysqld]下的下方加入

[mysqld] slow_query_log = ON log_queries_not_using_indexes = ON; slow_query_log_file = /usr/local/mysql/data/slow.log long_query_time = 1

 

查看设置后的参数 show variables like 'slow_query%'; show variables like 'long_query__time'; 二. 慢查询日志记录的内容 Time Id Command Argument # Time: 2019-01-08T04:12:09.269315Z # User@Host: h5_test[h5_test] @ localhost [::1] Id: 12 # Query_time: 0.000831 Lock_time: 0.000198 Rows_sent: 1 Rows_examined: 3 use mc_productdb; SET timestamp=1546920729; SELECT t.customer_id,t.title,t.content FROM ( SELECT customer_id FROM product_comment WHERE product_id =199726 AND audit_status = 1 LIMIT 0,15 )a JOIN product_comment t ON a.customer_id = t.comment_id;

Time：执行查询的日期时间
User@Host：执行查询的用户和客户端IP
Id：是执行查询的线程Id
Query_time：SQL执行所消耗的时间
Lock_time：执行查询对记录锁定的时间
Rows_sent：查询返回的行数
Rows_examined：为了返回查询的数据所读取的行数

三. 如何分析慢查询日志 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

由于慢查询日志中会含有大量的重复的SQL,为了方便，可以通过mysql提供的命令行工具 mysqldumpslow 来分析日志

$ mysqldumpslow.pl slow_log.log Reading mysql slow query log from slow_log.log Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), 0users@0hosts C:\Program Files\MySQL\MySQL Server N.N\bin\mysqld.exe, Version: N.N.N-log (MySQL Community Server (GPL)). started with: TCP Port: N, Named Pipe: MySQL # Time: N-N-08T04:N:N.269315Z # User@Host: h5_test[h5_test] @ localhost [::N] Id: N # Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N use mc_productdb; SET timestamp=N; SELECT t.customer_id,t.title,t.content FROM ( SELECT customer_id FROM product_comment WHERE product_id =N AND audit_status = N LIMIT N,N )a JOIN product_comment t ON a.customer_id = t.comment_id

与慢查询日志中记录的数据是相似的，只是多出了一行Count，这一行记录的是这条SQL在记录慢查询日志期间的执行次数，如果一个SQL多次被执行，用这个命令分析时，只会出现一个SQL日志，Count里的数值代表执行次数，其他数字为了合并表示用N代替。

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