comet_partitioning.rs

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use arrow::row::{OwnedRow, RowConverter};
use datafusion::physical_expr::{LexOrdering, PhysicalExpr};
use std::sync::Arc;

#[derive(Debug, Clone)]
pub enum CometPartitioning {
    SinglePartition,
    /// Allocate rows based on a hash of one of more expressions and the specified number of
    /// partitions. Args are 1) the expression to hash on, and 2) the number of partitions.
    Hash(Vec<Arc<dyn PhysicalExpr>>, usize),
    /// Allocate rows based on the lexical order of one of more expressions and the specified number of
    /// partitions. Args are 1) the LexOrdering to use to compare values and split into partitions,
    /// 2) the number of partitions, 3) the RowConverter used to view incoming RecordBatches as Arrow
    /// Rows for comparing to 4) OwnedRows that represent the boundaries of each partition, used with
    /// LexOrdering to bin each value in the RecordBatch to a partition.
    RangePartitioning(LexOrdering, usize, Arc<RowConverter>, Vec<OwnedRow>),
    /// Round robin partitioning. Distributes rows across partitions by sorting them by hash
    /// (computed from columns) and then assigning partitions sequentially. Args are:
    /// 1) number of partitions, 2) max columns to hash (0 means no limit).
    RoundRobin(usize, usize),
}

impl CometPartitioning {
    pub fn partition_count(&self) -> usize {
        use CometPartitioning::*;
        match self {
            SinglePartition => 1,
            Hash(_, n) | RangePartitioning(_, n, _, _) | RoundRobin(n, _) => *n,
        }
    }
}

pub(super) fn pmod(hash: u32, n: usize) -> usize {
    let hash = hash as i32;
    let n = n as i32;
    let r = hash % n;
    let result = if r < 0 { (r + n) % n } else { r };
    result as usize
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_pmod() {
        let i: Vec<u32> = vec![0x99f0149d, 0x9c67b85d, 0xc8008529, 0xa05b5d7b, 0xcd1e64fb];
        let result = i.into_iter().map(|i| pmod(i, 200)).collect::<Vec<usize>>();

        // expected partition from Spark with n=200
        let expected = vec![69, 5, 193, 171, 115];
        assert_eq!(result, expected);
    }
}