# 5.5 慢查询实战分析

## 5.5.1 慢查询相关的配置参数

* `slowlog-log-slower-than`:单位为微秒.超过该参数指定时长的查询会记录到日志中
* `slowlog-max-len`:在慢查询日志中可以记录的日志条数.当慢查询日志的数量已经到达该参数时,每有一条新的慢查询日志写入,就会有最老的一条日志被删除

例:设置慢查询的时长和慢查询日志的条数

```
127.0.0.1:6379> CONFIG SET slowlog-log-slower-than 1
OK
127.0.0.1:6379> CONFIG SET slowlog-max-len 100
OK
127.0.0.1:6379> CONFIG REWRITE
OK
```

此时配置文件内容如下:

```
# Generated by CONFIG REWRITE
slowlog-max-len 100
slowlog-log-slower-than 1
save 3600 1
save 300 100
save 60 10000
user default on nopass ~* &* +@all
dir "/redis-6.2.13"
```

## 5.5.2 用`SLOWLOG GET`命令观察慢查询

* `SLOWLOG GET`:返回所有的慢查询日志

```
127.0.0.1:6379> SET name Peter
OK
127.0.0.1:6379> GET name
"Peter"
```

```
127.0.0.1:6379> SLOWLOG GET
1) 1) (integer) 4
   2) (integer) 1692022815
   3) (integer) 3
   4) 1) "GET"
      2) "name"
   5) "127.0.0.1:57267"
   6) ""
2) 1) (integer) 3
   2) (integer) 1692022811
   3) (integer) 18
   4) 1) "SET"
      2) "name"
      3) "Peter"
   5) "127.0.0.1:57267"
   6) ""
3) 1) (integer) 2
   2) (integer) 1692022564
   3) (integer) 6865
   4) 1) "CONFIG"
      2) "REWRITE"
   5) "127.0.0.1:57267"
   6) ""
4) 1) (integer) 1
   2) (integer) 1692022560
   3) (integer) 5
   4) 1) "CONFIG"
      2) "SET"
      3) "slowlog-max-len"
      4) "100"
   5) "127.0.0.1:57267"
   6) ""
5) 1) (integer) 0
   2) (integer) 1692022556
   3) (integer) 13
   4) 1) "CONFIG"
      2) "SET"
      3) "slowlog-log-slower-than"
      4) "1"
   5) "127.0.0.1:57267"
   6) ""
```

我们以`GET name`命令的慢查询日志为例:

* `1) (integer) 4`:表示慢查询日志ID
* `2) (integer) 1692022815`:命令运行时的时间戳
* `3) (integer) 3`:命令运行的时长.单位为微秒
* `4) 1) "GET" 2) "name"`:一个数组.其中第一个元素是执行的命令,后续的元素是命令的参数
* `5) "127.0.0.1:57267"`:客户端地址和端口
* `6) ""`:客户端名称

## 5.5.3 慢查询相关命令

* `SLOWLOG GET n`:查看指定最新的n条慢查询日志

```
127.0.0.1:6379> SLOWLOG GET 1
1) 1) (integer) 5
   2) (integer) 1692022854
   3) (integer) 16
   4) 1) "SLOWLOG"
      2) "GET"
   5) "127.0.0.1:57267"
   6) ""
```

* `SLOWLOG LEN`:获取慢查询日志的长度

```
127.0.0.1:6379> SLOWLOG LEN
(integer) 9
```

* `SLOWLOG RESET`:清空慢查询日志

```
127.0.0.1:6379> SLOWLOG RESET
OK
127.0.0.1:6379> SLOWLOG LEN
(integer) 1
```

注:此处有1条慢查询日志是因为慢查询阈值设置的太低,导致`SLOWLOG LEN`也成为了慢查询


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