How does the size of a Map data structure increase?

In Go, the data structure map is implemented as a hash table with dynamic resizing. When adding new elements, if the load factor of the map reaches a certain threshold (usually around 6.5 elements per bucket), the size is increased (rehash) — a new hash table with more buckets is created, and all existing elements are redistributed across the new buckets.

This process happens automatically and transparently to the user. Increasing the size helps maintain a low collision probability and high performance of search and insert operations.

It can be roughly illustrated as follows:

m := make(map[string]int)
m["a"] = 1
// When adding a large number of elements, the map automatically increases its internal buffer
for i := 0; i < 1000; i++ {
    m[fmt.Sprintf("key%d", i)] = i
}

Internally, the Go runtime monitors the load and increases the map size as needed.