1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
use std::fmt::Debug;
use std::marker;
use crate::index::{SegmentId, SegmentMeta};
/// Set of segment suggested for a merge.
#[derive(Debug, Clone)]
pub struct MergeCandidate(pub Vec<SegmentId>);
/// The `MergePolicy` defines which segments should be merged.
///
/// Every time the list of segments changes, the segment updater
/// asks the merge policy if some segments should be merged.
pub trait MergePolicy: marker::Send + marker::Sync + Debug {
/// Given the list of segment metas, returns the list of merge candidates.
///
/// This call happens on the segment updater thread, and will block
/// other segment updates, so all implementations should happen rapidly.
fn compute_merge_candidates(&self, segments: &[SegmentMeta]) -> Vec<MergeCandidate>;
}
/// Never merge segments.
#[derive(Debug, Clone)]
pub struct NoMergePolicy;
impl Default for NoMergePolicy {
fn default() -> NoMergePolicy {
NoMergePolicy
}
}
impl MergePolicy for NoMergePolicy {
fn compute_merge_candidates(&self, _segments: &[SegmentMeta]) -> Vec<MergeCandidate> {
Vec::new()
}
}
#[cfg(test)]
pub mod tests {
use super::*;
/// `MergePolicy` useful for test purposes.
///
/// Every time there is more than one segment,
/// it will suggest to merge them.
#[derive(Debug, Clone)]
pub struct MergeWheneverPossible;
impl MergePolicy for MergeWheneverPossible {
fn compute_merge_candidates(&self, segment_metas: &[SegmentMeta]) -> Vec<MergeCandidate> {
let segment_ids = segment_metas
.iter()
.map(|segment_meta| segment_meta.id())
.collect::<Vec<SegmentId>>();
if segment_ids.len() > 1 {
vec![MergeCandidate(segment_ids)]
} else {
vec![]
}
}
}
}