Cost of a bool slice in Go
How much memory do 10 million bools take up?
Short answer
10MB. This is 8x as large as the number of bits that I actually care about.
Details
In Go all elements of a slice are addressable. The smallest addressable unit being the byte, a slice of bools looks in memory like a contiguous sequence of bytes, containing only 1 useful bit per byte.
The slice header itself (1 pointer + 2 integers) is negligible: its memory occupancy is dwarfed by the size of the backing array.
I suspected that on my 64-bit computer, the minimal addressable unit would be a 64-bit word, incurring a 64x overhead for each useful bit! Fortunately, bytes are still individually addressable, keeping the overhead to 8x.
If you’re worried about such a waste of memory, have a look at 7 ways to implement a Bit set in Go to learn about more compact options to store a large number of bits.
