I need to create as large arrays as possible in a numerical application. What is the largest array|vec index size in Rust?

The maximum length is isize::MAX / size_of::<T>() where T is the element type of your array. However, for large arrays, it is generally recommended to use a Vec.

What would that be for an array of unsigned 64-bit elements and unsigned 8-bit elements? I really want to create an array of size 2**64 - 1 elements of any type. Is that possible?

I'm not currently memory limited, I'm array|vec index limited. I want eventually the capacity to do UInt64::MAX (for a distributed system) I need now to be able to go over Int32::MAX elements on my laptop. I just need to know the MAX limit so I know how I have to architect my system resources.

[image] jzakiya: I want eventually the capacity to do UInt64::MAX (for a distributed system) That doesn't sound like an array or vector. Other kinds of collections can have their own restrictions. E.g. there's nothing stopping you from using a HashMap<u64, YourType>. [image] jzakiya: I n…

On x86-64 even though pointers are 64 bits you can't address that much memory. See the osdev wiki .

I have a 64-bit cpu|system, so I can address and array|vec up to (2**63 - 1) elements. Correct?

If the element size is zero, then you can have a vector of length 2^63-1, yes. fn main() { let vec = vec![(); 9223372036854775807]; println!("{}", vec.len()); } But if you want actual data in the vector, then no. Then creating the vector will fail because it is too large.

Thank you for confirming the answer. I know what I'm doing, and why.

[image] alice: That would take 18 million terabytes of RAM. You don't have that much memory. Yeah, but it would only cost 83.5 Billion dollars :slight_smile: <a href="https://www.amazon.com/8x128GB-DDR4-3200-PC4-25600-NEMIX-RAM/dp/B08F2RN2KQ/ref=sr_1_3?dib=eyJ2IjoiMSJ9.ObzrlEKGJlOYDBx4SUd5KJCeitc3Vkcyn7eaHIjDWmcOKq-RObUUrAghIYFiCFHMck1qdPE6DlyovZ8v7BLDyeD2Hl5sc4DqtlSdnz2ubBtp1_wCjqkPsUvM1Yh6QxQOEfM-hHF7GiR6xkO1ab3pX5UjZcO0FCU745Fyg6wtEjmjaePaa13668ite-3fWRo__WZqoMkF-Fk-WLDWw-PORv1d8wZlnmsGYIMILz_6qoc.SsUoji85XFaMkCpKpw_RqhoScYup2s9k-y3J2xscfDw&dib_tag=se&keywords=1TB%2BRAM&qid=1708357796&sr=8-3&th=1" rel="noopener nofollow ugc">Amazon

What is MAX array size?

alice February 19, 2024, 3:31pm 4

That would take 18 million terabytes of RAM. You don't have that much memory.

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What is MAX array size?

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