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 |
package main
import (
"github.com/go-redis/redis"
"fmt"
"time"
)
func main() {
client := redis.NewClient(&redis.Options{
Addr: "localhost:6379",
Password: "",
DB: 0,
ReadTimeout: 1000 * 1000 * 1000 * 60 * 60 * 24,
WriteTimeout: 1000 * 1000 * 1000 * 60 * 60 * 24,
})
maxLength := int64(10000 * 100)
for n := int64(1); n <= maxLength; n *= 10 {
fmt.Println("Set个数", n)
TestDelBigSet(client, n)
TestExpireBigSet(client, n)
TestUnlinkBigSet(client, n)
fmt.Println()
}
}
func TestDelBigSet(client *redis.Client, count int64) {
redisKey := fmt.Sprintf("%s%d", "del:", time.Now().Nanosecond())
for n := int64(0); n < count; n++ {
err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err()
if err != nil {
panic(err)
}
}
startTime := CurrentTimestampInMicroSecond()
client.Del(redisKey)
endTime := CurrentTimestampInMicroSecond()
fmt.Println("Del", endTime-startTime)
}
func TestUnlinkBigSet(client *redis.Client, count int64) {
redisKey := fmt.Sprintf("%s%d", "unlink:", time.Now().Nanosecond())
for n := int64(0); n < count; n++ {
err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err()
if err != nil {
panic(err)
}
}
startTime := CurrentTimestampInMicroSecond()
client.Unlink(redisKey)
endTime := CurrentTimestampInMicroSecond()
fmt.Println("Unlink", endTime-startTime)
}
func TestExpireBigSet(client *redis.Client, count int64) {
redisKey := fmt.Sprintf("%s%d", "expire:", time.Now().Nanosecond())
for n := int64(0); n < count; n++ {
err := client.SAdd(redisKey, fmt.Sprintf("%d", n)).Err()
if err != nil {
panic(err)
}
}
startTime := CurrentTimestampInMicroSecond()
client.Expire(redisKey, 0)
endTime := CurrentTimestampInMicroSecond()
fmt.Println("Expire", endTime-startTime)
}
func CurrentTimestampInMicroSecond() int64 {
return time.Now().UnixNano() / 1000
}