Function compute_sampled_splits 

async fn compute_sampled_splits(
    tx: &mut Transaction<'_>,
    table: &MySqlTableName,
    raw_col: &str,
    scalar_type: &SqlScalarType,
    worker_count: usize,
    row_count: u64,
    settings: &PartitionSettings,
) -> Result<Option<PkBoundaries>, TransientError>

Attempts to compute roughly even boundaries for primary keys. Returns None if the column type is unsupported or boundaries couldn’t be estimated for some reason. Currently only supports CHAR/VARCHAR columns with up to 768 characters with utf8mb4_bin collation.