How to Accurately Calculate the Memory Footprint of a Go Map?

Calculating Memory Footprint of a Map in Go

Determining the memory consumption of a map is essential for resource management and optimization. However, computing the byte length of a map in Go is not a straightforward task.

Go's "encoding/binary" package provides the Size function for computing the memory footprint of slices and "fixed values," but it does not support maps. Manually inferring the type and size of key-value pairs in the map would be tedious and potentially inaccurate.

Delving into the Map Structure

The solution lies in understanding the internal structure of a map. A Go map is represented by a header (hmap) followed by an array of buckets (bmap). The hmap contains essential information such as the count of live cells (map size), hash seed, and the number of buckets.

Calculating Map Memory Footprint

The memory footprint of a map can be calculated as follows:

1. Size of the hmap header: unsafe.Sizeof(hmap)
2. Memory consumed by keys: len(map) * 8
3. Memory consumed by values: len(map) 8 unsafe.Sizeof(value_type)
4. Memory overhead for buckets: len(map) 8 unsafe.Sizeof(key_type)

Example Code

The following code demonstrates the calculation of a map's memory footprint:

import (
    "fmt"
    "unsafe"
)

type MyMap map[string]int

func main() {
    m := MyMap{"key1": 1, "key2": 2}

    keySize := unsafe.Sizeof(string("key1"))
    valueSize := unsafe.Sizeof(1)
    headerSize := unsafe.Sizeof(hmap{})
    numKeys := len(m)

    memoryFootprint := headerSize + (numKeys * 8) + (numKeys * 8 * valueSize) + (numKeys * 8 * keySize)

    fmt.Printf("Memory footprint of the map: %d bytes\n", memoryFootprint)
}

This code effectively computes the memory footprint of the MyMap, including the header, keys, values, and bucket overhead.

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