Redis刪除大Key
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這裡說的大key是指包含很多元素的set,sorted set,list和hash。
刪除操作，我們一般想到有2種，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).
如果要刪除的key是一個集合，包含了很多元素，那麼DEL
時的耗時和元素個數成正比，所以如果直接DEL
，會很慢。
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).
想著expire會不會可以不是直接刪除，可惜官網的描述讓我心灰意冷，如果expire後指定的timeout不是正數，也就是<=0，那其實就是DEL
。
一點一點刪
我們知道Redis的工作執行緒是單執行緒的，如果一個command堵塞了，那所有請求都會超時，這時候，一些騷操作也許可以幫助你。
其實如果想刪除key，可以分解成2個目的，1：不想讓其他人訪問到這個key，2：釋放空間。
那其實我們可以分解成兩步，先用RENAME
把原先的key rename成另一個key，比如：
RENAME userInfo:123 "deleteKey:userInfo:123"
然後可以慢慢去刪"deleteKey:userInfo:123"，如果是set，那麼可以用SREM
慢慢刪，最後再用DEL
徹底刪掉。
這裡可以搞個task去SCAN deleteKey:*
，然後慢慢刪除。
UNLINK
Redis 4.0.0提供了一個更加方便的命令
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
其實是直接返回，然後在後臺執行緒慢慢刪除。
如果你的Redis版本>=4.0.0，那麼強烈建議使用UNLINK
來刪除。
刪除耗時測試結果
單位：微秒
|Set個數|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個數", 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
}