redis和mysql都存在对于慢查询的日志记录，下面将叙述一下两者的慢查询。
一，redis[1]redis的慢查询日志本质上是一个list对象，不过redis并没有提供慢查询日志的key。开发者可以通过下列命令查询慢查询日志：
#获得慢查询日志，n可以指定条数slowlog get [n]#慢查询日志列表当前的长度slowlog len#慢查询日志重置slowlog resetredis提供了slowlog-log-slower-tan和slowlog-max-len配置，slowlog-log-slower-than是慢查询日志的阈值，单位是微秒，默认值是10000；slowlog-max-len是慢查询日志最多存储多少条。
我们可以修改配置文件来修改上述配置，也可以通过在客户端动态修改，如
#修改配置，重启后失效config set slowlog-max-len 1000#将配置持久化到配置文件config rewriteredis的慢查询日志本质上是一个队列或者说列表，有固定的长度限制，如果超出长度，会丢失一部分慢查询日志。如果想要将慢查询日志持久化，可以通过定时任务将慢查询日志的结果持久化到其他存储中[1]。
二，mysql进入mysql客户端，
查询是否开启慢查询日志：
#slow_query_log，是否开启了慢查询日志，当前状态为OFFmysql> show variables like 'slow_query_log'-> ;+----------------+-------+| Variable_name | Value |+----------------+-------+| slow_query_log | OFF |+----------------+-------+1 row in set (0.01 sec)#开启慢查询日志mysql> set global slow_query_log=on;Query OK, 0 rows affected (0.00 sec)mysql> show variables like 'slow_query_log';+----------------+-------+| Variable_name | Value |+----------------+-------+| slow_query_log | ON |+----------------+-------+1 row in set (0.00 sec)慢查询日志阈值，单位为秒，默认10秒
mysql> show variables like 'long_query_time';+-----------------+-----------+| Variable_name | Value |+-----------------+-----------+| long_query_time | 10.000000 |+-----------------+-----------+1 row in set (0.00 sec)慢查询日志路径
mysql> show variables like 'slow_query_log_file';+---------------------+-----------------------------------+| Variable_name | Value |+---------------------+-----------------------------------+| slow_query_log_file | /var/lib/mysql/localhost-slow.log |+---------------------+-----------------------------------+1 row in set (0.00 sec)是否在慢查询日志中记录没有使用索引的SQL
mysql> show variables like 'log_queries_not_using_indexes';+-------------------------------+-------+| Variable_name | Value |+-------------------------------+-------+| log_queries_not_using_indexes | OFF |+-------------------------------+-------+1 row in set (0.00 sec)这里为了演示，我们把慢查询日志的阈值调为0s，这样任何sql都会被判断为慢查询并记录在日志中。
mysql> set global long_query_time=0;Query OK, 0 rows affected (0.00 sec)我们开启另外一个shell，去查看慢查询日志，可以看到此时慢查询日志多了一些日志
#没有开启慢查询日志时，日志文件中没有记录[root@localhost usr]# cat /var/lib/mysql/localhost-slow.log /usr/sbin/mysqld, Version: 5.7.44 (MySQL Community Server (GPL)). started with:Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sockTime Id Command Argument[root@localhost usr]# vi /var/lib/mysql/localhost-slow.log ;#开启慢查询日志后，日志中有了记录[root@localhost usr]# cat /var/lib/mysql/localhost-slow.log /usr/sbin/mysqld, Version: 5.7.44 (MySQL Community Server (GPL)). started with:Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sockTime Id Command Argument# Time: 2023-12-15T12:08:27.357678Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000328 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0SET timestamp=1702642107;select @@version_comment limit 1;# Time: 2023-12-15T12:09:02.503218Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.003156 Lock_time: 0.000522 Rows_sent: 1 Rows_examined: 1052SET timestamp=1702642142;show variables like 'slow_query_log_file';# Time: 2023-12-15T12:10:19.797352Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000141 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642219;set global slow_query_log = on;# Time: 2023-12-15T12:10:33.596783Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.001013 Lock_time: 0.000140 Rows_sent: 1 Rows_examined: 1052SET timestamp=1702642233;show variables like 'slow_query_log';# Time: 2023-12-15T12:10:59.163838Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000086 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642259;set global long_query_time = 0;# Time: 2023-12-15T12:11:08.379448Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000115 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642268;select * from emp;# Time: 2023-12-15T12:11:23.468288Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000652 Lock_time: 0.000120 Rows_sent: 5 Rows_examined: 5SET timestamp=1702642283;show databases;# Time: 2023-12-15T12:11:27.571064Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000131 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0SET timestamp=1702642287;SELECT DATABASE();# Time: 2023-12-15T12:11:27.571279Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000039 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0use locktest;SET timestamp=1702642287;# administrator command: Init DB;# Time: 2023-12-15T12:11:27.573106Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000214 Lock_time: 0.000075 Rows_sent: 5 Rows_examined: 5SET timestamp=1702642287;show databases;# Time: 2023-12-15T12:11:27.573360Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000081 Lock_time: 0.000029 Rows_sent: 4 Rows_examined: 4SET timestamp=1702642287;show tables;# Time: 2023-12-15T12:11:27.573615Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000143 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642287;;# Time: 2023-12-15T12:11:27.573756Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000068 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642287;;# Time: 2023-12-15T12:11:27.573919Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000044 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642287;;# Time: 2023-12-15T12:11:27.573998Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000035 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0SET timestamp=1702642287;;# Time: 2023-12-15T12:11:32.483758Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000207 Lock_time: 0.000108 Rows_sent: 4 Rows_examined: 4SET timestamp=1702642292;show tables;# Time: 2023-12-15T12:11:37.555298Z# User@Host: root[root] @ localhost [] Id: 6# Query_time: 0.000271 Lock_time: 0.000078 Rows_sent: 12 Rows_examined: 12SET timestamp=1702642297;select * from emp;其中Query_time为查询时间，Lock_time为等待锁的阻塞时间，加起来是在Mysql中查询使用的时间。
参考文章： [1]，redis开发与运维，ISBN 978-7-111-55797-5
