Is there any document about the amount of memory occupied by the basic types of Motoko canister?
such as a Nat8 array with n size, a principal, a enum, a HashMap and so on.
In the world of canisters and cycles… every byte counts.
No, I don’t think such a document exists. The ASCII-art and comments in motoko/compile.ml at master · dfinity/motoko · GitHub is maybe the best place right now, but this is of course written with the compiler developer in mind. And there are a bunch of optimizations (e.g. small numbers are not stored as pointed-to objects, but “instead of” the pointer) that make such predictions harder.
To answer your concrete questions:
- A
[Nat8]with n elements will take 8+4×n bytes. - A principal is represented the same way as a blog, so if it is n bytes (binary representation, not the textual format), then up to 8+n+3 bytes.
- An variant is 12 bytes (plus whatever is stored inside the tag). If it’s strictly an enum (i.e. only
()stored inside), then the()is “free”. - A hashmap is more complicated, but it’s not a basic type, so I’ll punt on that one
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Thanks for your great answer,
How about Nat32, Nat64, Nat, Int, Text, List, Option ?T, Char
-
Nat32,Char: 8 bytes -
Int64: 12 bytes -
NatandInt: “free” if smaller than 2^30, else at least 20 bytes, up to arbitrary sizes -
TextandBlob: up to 8+n+3 bytes. -
opt: “free” unless you deal with the value?…?null -
Listis not a basic type. Probably 12*n
Free means that it’s stored inside the containing data structure without extra allocation.
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Does this also apply to the RUST canister?
No, he’s talking about Motoko only.
Just curious: why does a Nat32 occupy 8 bytes?
Every heap-allocated object has a 1-word (4-bytes) header, followed by the payload, which, in this case, is 4 bytes:
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Does it specific only for motoko compiled module? I mean if I build a module using rust what size whould be for byte array ?