Group By no longer supported in Rust WASM

[brettsaunders21]

Group By no longer supported in Rust WASM

[ritchie46]

Hmm... The usize should be changed to u64.

[daBlesr]

Hi @ritchie46, not sure if I understand, usize is architecture agnostic right? Which 'problematic' use of usize are you exactly referring to in the code?

[daBlesr]

I see that the offsets vector in RowsEncoded is casted later to i64 (after checking the types) and this causes the problem. Is your suggestion to change the type of offsets to Vec<u64>, such that they take the same number of bytes on memory?

[daBlesr]

I quickly checked the impact of the above, and the code becomes a bit less appealing using u64 as it will also require changes on encode.rs casting usize to u64. What do you think of the following, where offset<usize> (naturally) remains as-is:

let offsets = if std::mem::size_of::<usize>() % std::mem::size_of::<i64>() == 0 {
    // We can safely convert usize to i64
    bytemuck::cast_vec::<usize, i64>(offsets)
} else {
    offsets.iter().map(|&i| i as i64).collect()
};

It checks if it can simply convert, or in worst-case (for wasm) it will have some performance impact because it needs to cast the encoded rows.