场景介绍
热 key 是指用户访问一个 key 的 QPS 特别高，导致 Server 实例出现 CPU 负载突增或者不均的情况，如果未能及时发现和处理，可能导致服务性能下降，用户体验变差，进而可能引发大规模故障。
分析热 key 的方法有很多，本文专注于如何使用原生 redis-cli 工具，通过添加 --hotkeys 选项，可以快找出业务中的热 key。
前提条件
- ECS中已经安装了 Redis 4.0 以上版本；目的是为了使用 redis-cli 工具。
- 保证客户端与 redis 网络互通。
- Redis 实例的 maxmemory-policy 参数设置为 volatile-lfu 或 allkeys-lfu。
- 直连地址无法支持 object 命令，请使用其地址。
操作步骤
运行如下命令，可以在整个实例级别来发现热 key：
(base) [root@rudonx ~]# redis-cli -h xxxxxx.redis.ivolces.com -a xxxxx --hotkeys
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
# Scanning the entire keyspace to find hot keys as well as
# average sizes per key type. You can use -i 0.1 to sleep 0.1 sec
# per 100 SCAN commands (not usually needed).
[00.00%] Hot key '"key:{tag}:000000000158"' found so far with counter 23
[00.00%] Hot key '"key:{tag}:000000000102"' found so far with counter 20
[00.00%] Hot key '"key:{tag}:000000000082"' found so far with counter 26
[00.00%] Hot key '"key:{tag}:000000000126"' found so far with counter 23
[00.00%] Hot key '"key:{tag}:000000000081"' found so far with counter 23
[00.00%] Hot key '"key:{tag}:000000000186"' found so far with counter 21
[00.00%] Hot key '"key:{tag}:000000000148"' found so far with counter 22
[00.00%] Hot key '"key:{tag}:000000000049"' found so far with counter 26
[00.00%] Hot key '"key:{tag}:000000000122"' found so far with counter 19
[00.00%] Hot key '"key:{tag}:000000000165"' found so far with counter 21
.......
-------- summary -------
Sampled 200 keys in the keyspace!
hot key found with counter: 30 keyname: "key:{tag}:000000000137"
hot key found with counter: 30 keyname: "key:{tag}:000000000114"
hot key found with counter: 28 keyname: "key:{tag}:000000000143"
hot key found with counter: 27 keyname: "key:{tag}:000000000130"
hot key found with counter: 27 keyname: "key:{tag}:000000000175"
hot key found with counter: 26 keyname: "key:{tag}:000000000082"
hot key found with counter: 26 keyname: "key:{tag}:000000000049"
hot key found with counter: 26 keyname: "key:{tag}:000000000179"
hot key found with counter: 26 keyname: "key:{tag}:000000000133"
hot key found with counter: 26 keyname: "key:{tag}:000000000154"
hot key found with counter: 26 keyname: "key:{tag}:000000000038"
hot key found with counter: 26 keyname: "key:{tag}:000000000028"
hot key found with counter: 26 keyname: "key:{tag}:000000000194"
hot key found with counter: 26 keyname: "key:{tag}:000000000046"
hot key found with counter: 26 keyname: "key:{tag}:000000000139"
hot key found with counter: 26 keyname: "key:{tag}:000000000182"
参数解释
- -h：Redis 实例的地址。
- -a：指定 Redis 实例的密码。
- --hotkeys：进行热 key 分析。
报错解决
Error: ERR unknown command 'OBJECT'
解决方案：出现此错误是由于使用 redis 直连地址，不支持 OBJECT 命令导致，请使用其他地址类型。参考文档[1]
(base) [root@rudonx ~]# redis-cli -h xxxx-direct.redis.ivolces.com -a xxxx --hotkeys
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
# Scanning the entire keyspace to find hot keys as well as
# average sizes per key type. You can use -i 0.1 to sleep 0.1 sec
# per 100 SCAN commands (not usually needed).
Error: ERR unknown command 'OBJECT'
Error: ERR An LFU maxmemory policy is not selected
解决方案：Redis 实例的 maxmemory-policy 参数需要设置为 volatile-lfu 或 allkeys-lfu。
(base) [root@rudonx ~]# redis-cli -h xxxx-direct.redis.ivolces.com -a xxxx --hotkeys
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
# Scanning the entire keyspace to find hot keys as well as
# average sizes per key type. You can use -i 0.1 to sleep 0.1 sec
# per 100 SCAN commands (not usually needed).
Error: ERR An LFU maxmemory policy is not selected, access frequency not tracked. Please note that when switching between policies at runtime LRU and LFU data will take some time to adjust.
Couldn't determine DBSIZE!
解决方案：请检查网络联通性，密码的正确性。
(base) [root@rudonx ~]# redis-cli -h xxxx-direct.redis.ivolces.com -a xxxx --hotkeys
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
Couldn't determine DBSIZE!
