How Much Memory Does an Uninitialized Go Map Allocate?

Determining Memory Allocation for Uninitialized Go Maps

In JavaScript, when creating a map, the initial capacity is not explicitly specified. The allocated memory is implementation-dependent. This article explores how to determine memory allocation for such maps in Go.

Initial Memory Allocation

When a map is created without specifying the initial capacity, Go allocates a small amount of memory. This includes a header and an array of buckets.

Understanding Map Structure

According to Go's map type source code, a map comprises:

• A header (type hmap) with fields occupying 40 bytes
• An array of buckets (type bmap) with each bucket occupying 8 bytes

Calculation

For a 64-bit architecture, the initial memory allocation is as follows:

Header Fields: 40 bytes
Bucket Array (1 bucket): 8 bytes
---------------------------
Total: 48 bytes

Note:

The exact memory allocation may vary depending on factors such as the operating system and architecture.

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