Golang 中的池化映射

Question

我很好奇是否有人尝试过 pool maps in Go before? I've read about pooling buffers previously, and I was wondering if by similar reasoning it could make sense to pool maps if one has to create and destroy them frequently or if there was any reason why, a priori, it might not be efficient. When a map is returned to the pool, one would have to iterate through it and delete all elements, but it seems a popular recommendation is to create a new map instead of deleting the entries in a map which has already been allocated and reusing it 这让我觉得合并地图可能没有那么有益。

Answer 1

如果您的映射通过删除或添加条目改变了（很多）大小，这将导致新的分配，并且将它们集中起来没有任何好处。

如果您的地图大小不会改变，而只有键的值会改变，那么池化将是一个成功的优化。

当您阅读 table-like 结构时，例如 CSV 文件或数据库表，这将很有效。每行将包含完全相同的列，因此您无需清除任何条目。

当运行和 go test -benchmem -bench . 到

时，下面的基准显示没有分配

package mappool

import "testing"

const SIZE = 1000000

func BenchmarkMap(b *testing.B) {
    m := make(map[int]int)

    for i := 0; i < SIZE; i++ {
        m[i] = i
    }

    b.ResetTimer()

    for i := 0; i < b.N; i++ {
        for i := 0; i < SIZE; i++ {
            m[i] = m[i] + 1
        }
    }
}

Answer 2

正如@Grzegorz Żur 所说，如果您的贴图大小变化不大，那么池化会很有帮助。为了测试这一点，我做了一个基准，其中池化胜出。我机器上的输出是：

Pool time: 115.977µs
No-pool time: 160.828µs

基准代码：

package main

import (
    "fmt"
    "math/rand"
    "time"
)

const BenchIters = 1000

func main() {
    pool := map[int]int{}
    poolTime := benchmark(func() {
        useMapForSomething(pool)

        // Return to pool by clearing the map.
        for key := range pool {
            delete(pool, key)
        }
    })

    nopoolTime := benchmark(func() {
        useMapForSomething(map[int]int{})
    })

    fmt.Println("Pool time:", poolTime)
    fmt.Println("No-pool time:", nopoolTime)
}

func useMapForSomething(m map[int]int) {
    for i := 0; i < 1000; i++ {
        m[rand.Intn(300)] += 5
    }
}

// benchmark measures how long f takes, on average.
func benchmark(f func()) time.Duration {
    start := time.Now().UnixNano()
    for i := 0; i < BenchIters; i++ {
        f()
    }
    return time.Nanosecond * time.Duration((time.Now().UnixNano()-start)/BenchIters)
}

Golang 中的池化映射

Pooling Maps in Golang

hashmap

go

object-pooling