分析redis key的大小
bigKeys
这是redis-cli自带的一个命令。对整个redis进行扫描，寻找较大的key。例：
格式：redis-cli -h 服务端主机名或者IP地址 -p 端口 [-a password] --bigkeys
$ redis-cli -h 192.168.0.112 -p 6379 --bigkeys说明：
①该命令使用scan方式对key进行统计，所以使用时无需担心对redis造成阻塞。
②输出大概分为两部分，summary之上的部分，只是显示了扫描的过程。summary部分给出了每种数据结构中最大的Key。
③统计出的最大key只有string类型是以字节长度为衡量标准的。list,set,zset等都是以元素个数作为衡量标准，不能说明其占的内存就一定多。所以，如果你的Key主要以string类型存在，这种方法就比较适合。
输出内容：
# Scanning the entire keyspace to find biggest 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%] Biggest string found so far 'tx:manager:compensate:order-service:2019-01-25:eXC0yl5s.json' with 69032 bytes
[00.00%] Biggest hash found so far 'count' with 33 fields
[47.62%] Biggest set found so far 'menu:url' with 8 members
-------- summary -------
Sampled 21 keys in the keyspace!
Total key length in bytes is 743 (avg len 35.38)
Biggest string found 'tx:manager:compensate:order-service:2019-01-25:eXC0yl5s.json' has 69032 bytes
Biggest set found 'menu:url' has 8 members
Biggest hash found 'count' has 33 fields
14 strings with 274555 bytes (66.67% of keys, avg size 19611.07)
0 lists with 0 items (00.00% of keys, avg size 0.00)
1 sets with 8 members (04.76% of keys, avg size 8.00)
6 hashs with 39 fields (28.57% of keys, avg size 6.50)
0 zsets with 0 members (00.00% of keys, avg size 0.00)