clawsync/crates/clawhdf5-onion/benches/merkle_bench.rs

//! Criterion benchmarks for the revision Merkle tree.
//!
//! Groups:
//! - `merkle_index/build_tree/N`      — build tree from N revisions
//! - `merkle_index/diff_walk/N/D`     — diff walk with D differing revisions
//! - `merkle_index/serialise/N`       — serialise N-leaf tree
//! - `merkle_index/deserialise/N`     — deserialise N-leaf tree
//! - `merkle_index/serialised_size/N` — report bytes vs flat manifest
//!
//! Run:
//!   cargo bench -p clawhdf5-onion -- merkle_bench

use clawhdf5_onion::merkle::RevisionMerkleTree;
use criterion::{BenchmarkId, Criterion, black_box, criterion_group, criterion_main};

fn rev_hash(r: u64) -> [u8; 32] {
    *blake3::hash(&r.to_le_bytes()).as_bytes()
}

fn make_entries(n: usize) -> Vec<(u64, [u8; 32])> {
    (0..n as u64).map(|r| (r, rev_hash(r))).collect()
}

// ─────────────────────────────────────────────────────────────────────────────

fn bench_merkle(c: &mut Criterion) {
    let ns = [100usize, 1_000, 10_000];

    // ── Build ─────────────────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/build_tree");
    for &n in &ns {
        let entries = make_entries(n);
        group.bench_with_input(BenchmarkId::from_parameter(n), &entries, |b, e| {
            b.iter(|| RevisionMerkleTree::build(black_box(e)));
        });
    }
    group.finish();

    // ── Diff walk: D=0 (all match) ────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/diff_walk_d0");
    for &n in &ns {
        let tree = RevisionMerkleTree::build(&make_entries(n));
        group.bench_with_input(BenchmarkId::from_parameter(n), &tree, |b, t| {
            b.iter(|| t.diff_missing_revisions(black_box(t)));
        });
    }
    group.finish();

    // ── Diff walk: D=1 ───────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/diff_walk_d1");
    for &n in &ns {
        let full = RevisionMerkleTree::build(&make_entries(n));
        let minus1 = RevisionMerkleTree::build(&make_entries(n - 1));
        group.bench_with_input(
            BenchmarkId::from_parameter(n),
            &(full, minus1),
            |b, (f, m)| {
                b.iter(|| f.diff_missing_revisions(black_box(m)));
            },
        );
    }
    group.finish();

    // ── Diff walk: D=10 ──────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/diff_walk_d10");
    for &n in &ns {
        if n < 20 {
            continue;
        }
        let full = RevisionMerkleTree::build(&make_entries(n));
        let base = RevisionMerkleTree::build(&make_entries(n - 10));
        group.bench_with_input(
            BenchmarkId::from_parameter(n),
            &(full, base),
            |b, (f, base)| {
                b.iter(|| f.diff_missing_revisions(black_box(base)));
            },
        );
    }
    group.finish();

    // ── Diff walk: D=100 ─────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/diff_walk_d100");
    for &n in &[1_000usize, 10_000] {
        let full = RevisionMerkleTree::build(&make_entries(n));
        let base = RevisionMerkleTree::build(&make_entries(n - 100));
        group.bench_with_input(
            BenchmarkId::from_parameter(n),
            &(full, base),
            |b, (f, base)| {
                b.iter(|| f.diff_missing_revisions(black_box(base)));
            },
        );
    }
    group.finish();

    // ── Serialise ─────────────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/serialise");
    for &n in &ns {
        let tree = RevisionMerkleTree::build(&make_entries(n));
        group.bench_with_input(BenchmarkId::from_parameter(n), &tree, |b, t| {
            b.iter(|| black_box(t.serialise()));
        });
    }
    group.finish();

    // ── Deserialise ───────────────────────────────────────────────────────────
    let mut group = c.benchmark_group("merkle_index/deserialise");
    for &n in &ns {
        let bytes = RevisionMerkleTree::build(&make_entries(n)).serialise();
        group.bench_with_input(BenchmarkId::from_parameter(n), &bytes, |b, b_| {
            b.iter(|| RevisionMerkleTree::deserialise(black_box(b_)).unwrap());
        });
    }
    group.finish();

    // ── Serialised size report (not timed) ───────────────────────────────────
    println!("\n=== Serialised size vs flat manifest (N × 60 B) ===");
    println!(
        "{:>8}  {:>12}  {:>12}  {:>10}",
        "N", "Merkle (B)", "Flat (B)", "ratio"
    );
    for &n in &[10usize, 100, 1_000, 10_000] {
        let tree = RevisionMerkleTree::build(&make_entries(n));
        let merkle_sz = tree.serialise().len();
        let flat_sz = n * 60;
        println!(
            "{:>8}  {:>12}  {:>12}  {:>10.2}x",
            n,
            merkle_sz,
            flat_sz,
            flat_sz as f64 / merkle_sz as f64
        );
    }
}

criterion_group!(benches, bench_merkle);
criterion_main!(benches);