Function atm::utils::gen_partition_size

pub fn gen_partition_size(
    num_notes: f32, 
    length: i32, 
    max_file_count: f32, 
    partition_depth: i32
) -> u32

Calculate number of MIDI notes per partition.

Arguments

• num_notes: number of possible notes (duplicates allowed)
• length: length of generated MIDI sequences (see: gen_sequences)
• max_file_count: maximum number of files per partition (recommended <= 4K)
• partition_depth: number of partitions

Preconditions

• num_notes > 0
• length > 0
• max_files_count > 0
• partition_depth > 0
• partition_depth <= num_notes
• if num_noteslength <= max_file_count, partition_depth == 1

Examples

let partition_size = atm::utils::gen_partition_size(8.0, 12, 4096.0, 2);

// With these parameters, the calculation would be:
// https://www.wolframalpha.com/input/?i=ceil%28log64%28max%288%5E12%2F4096%2C+1%29%29%29
assert_eq!(4, partition_size)

Notes:

Most modern filesystems do not perform well with more than 4K files per folder, and XFS is no exception. In order to prevent overloading a single folder, we decided to partition sequences by their hash, which is just the integer representation of the MIDI notes in the sequence (see: libatm::MIDIFile::gen_hash), such that no folder would contain more than max_file_count number of files. The formula works as follows:

let N = num_notes^length (number of files to be generated)
let D = max(N / max_file_count, 1) (maximum number of directories to generate)
let B = num_notes^{partition_depth} (logarithm base)
partition_size = ceil(log_B(D))

NOTE: If num_notes is 1 or num_notes^length is less than or equal to max_file_count then the function will simply return length (see Preconditions above).