原文链接：https://www.dubby.cn/detail.html?id=9112
这里说的大key是指包含很多元素的set,sorted set,list和hash。
删除操作，我们一般想到有2种，del和expire。
DEL
Time complexity: O(N) where N is the number of keys that will be removed. When a key to remove holds a value other than a string, the individual complexity for this key is O(M) where M is the number of elements in the list, set, sorted set or hash. Removing a single key that holds a string value is O(1).
如果要删除的key是一个集合，包含了很多元素，那么DEL时的耗时和元素个数成正比，所以如果直接DEL，会很慢。
EXPIRE
Note that calling EXPIRE/PEXPIRE with a non-positive timeout or EXPIREAT/PEXPIREAT with a time in the past will result in the key being deleted rather than expired (accordingly, the emitted key event will be del, not expired).
想着expire会不会可以不是直接删除，可惜官网的描述让我心灰意冷，如果expire后指定的timeout不是正数，也就是<=0，那其实就是DEL。
一点一点删
我们知道Redis的工作线程是单线程的，如果一个command堵塞了，那所有请求都会超时，这时候，一些骚操作也许可以帮助你。
其实如果想删除key，可以分解成2个目的，1：不想让其他人访问到这个key，2：释放空间。
那其实我们可以分解成两步，先用RENAME把原先的key rename成另一个key，比如：
RENAME userInfo:123 "deleteKey:userInfo:123"
然后可以慢慢去删"deleteKey:userInfo:123"，如果是set，那么可以用SREM慢慢删，最后再用DEL彻底删掉。
这里可以搞个task去
SCAN deleteKey:*，然后慢慢删除。
UNLINK
Redis 4.0.0提供了一个更加方便的命令
Available since 4.0.0.
Time complexity: O(1) for each key removed regardless of its size. Then the command does O(N) work in a different thread in order to reclaim memory, where N is the number of allocations the deleted objects where composed of.
UNLINK其实是直接返回，然后在后台线程慢慢删除。
如果你的Redis版本>=4.0.0，那么强烈建议使用UNLINK来删除。
删除耗时测试结果
单位：微秒
Set个数
DEL
EXPIRE
UNLINK
1
90
97
75
10
79
67
100
100
51
49
47
1000
303
296
49
10000
2773
2592
52
100000
31210
33157
51
1000000
549388
501536
62
1package main 2 3import ( 4 "github.com/go-redis/redis" 5 "fmt" 6 "time" 7) 8 9func main() { 10 client := redis.NewClient(&redis.Options{ 11 Addr: "localhost:6379", 12 Password: "", 13 DB: 0, 14 ReadTimeout: 1000 * 1000 * 1000 * 60 * 60 * 24, 15 WriteTimeout: 1000 * 1000 * 1000 * 60 * 60 * 24, 16 }) 17 18 maxLength := int64(10000 * 100) 19 20 for n := int64(1); n <= maxLength; n *= 10 { 21 fmt.Println("Set个数", n) 22 TestDelBigSet(client, n) 23 TestExpireBigSet(client, n) 24 TestUnlinkBigSet(client, n) 25 fmt.Println() 26 } 27} 28 29func TestDelBigSet(client *redis.Client, count int64) { 30 redisKey := fmt.Sprintf("%s%d", "del:", time.Now().Nanosecond()) 31 32 for n := int64(0); n < count; n++ { 33 err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err() 34 if err != nil { 35 panic(err) 36 } 37 } 38 39 startTime := CurrentTimestampInMicroSecond() 40 client.Del(redisKey) 41 endTime := CurrentTimestampInMicroSecond() 42 43 fmt.Println("Del", endTime-startTime) 44} 45 46func TestUnlinkBigSet(client *redis.Client, count int64) { 47 redisKey := fmt.Sprintf("%s%d", "unlink:", time.Now().Nanosecond()) 48 49 for n := int64(0); n < count; n++ { 50 err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err() 51 if err != nil { 52 panic(err) 53 } 54 } 55 startTime := CurrentTimestampInMicroSecond() 56 client.Unlink(redisKey) 57 endTime := CurrentTimestampInMicroSecond() 58 59 fmt.Println("Unlink", endTime-startTime) 60} 61 62func TestExpireBigSet(client *redis.Client, count int64) { 63 redisKey := fmt.Sprintf("%s%d", "expire:", time.Now().Nanosecond()) 64 65 for n := int64(0); n < count; n++ { 66 err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err() 67 if err != nil { 68 panic(err) 69 } 70 } 71 startTime := CurrentTimestampInMicroSecond() 72 client.Expire(redisKey, 0) 73 endTime := CurrentTimestampInMicroSecond() 74 75 fmt.Println("Expire", endTime-startTime) 76} 77 78func CurrentTimestampInMicroSecond() int64 { 79 return time.Now().UnixNano() / 1000 80}