(6) MySQL慢查询日志的使用

时间:2021-06-29 02:34:20

一. 设置方法

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