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craft-metadata: interleave the linear-time scan test's runs

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The best-of-three ratio still failed once under load. The test now alternates
five runs of 50 000 and 200 000 attributes and compares the fastest of each,
so a burst of load slows both sizes. Six runs at load average 55 gave ratios
of 3.9 to 5.4 against the bound of 10.
This commit is contained in:
Dylan M. Taylor
2026-11-12 00:35:29 +00:00
parent 0cada31c49
commit 94db116f03
1 changed files with 14 additions and 14 deletions
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crates/metadata/src/xmp_merge.rs
+14 -14
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@@ -466,7 +466,7 @@ mod tests {
fn many_attributes_scan_in_linear_time() {
// quick-xml's duplicate-name check compares each attribute with all earlier ones: 200 000 attributes on
// one description took over 20 s to scan, about 30 ms with the set. Four times the attributes must take
// about four times as long, not sixteen. A ratio of best-of-three times holds on a loaded machine, where
// about four times as long, not sixteen. A ratio of the fastest runs holds on a loaded machine, where
// a fixed bound does not.
let packet = |n: usize| {
let mut s = String::from(
@@ -479,20 +479,20 @@ mod tests {
s.push_str("/></rdf:RDF></x:xmpmeta>");
s
};
let best = |n: usize| {
let s = packet(n);
(0..3)
.map(|_| {
let t = std::time::Instant::now();
let found = scan(&s, &[]).unwrap();
let took = t.elapsed();
assert_eq!(found.descs[0].attrs.len(), n + 2, "every attribute is read");
took
})
.min()
.unwrap_or_default()
let run = |s: &str, n: usize| {
let t = std::time::Instant::now();
let found = scan(s, &[]).unwrap();
let took = t.elapsed();
assert_eq!(found.descs[0].attrs.len(), n + 2, "every attribute is read");
took
};
let (small, large) = (best(25_000), best(100_000));
let (n, small_packet, large_packet) = (50_000, packet(50_000), packet(200_000));
// interleaved, so a burst of load slows both sizes rather than one; the fastest run of each counts
let (mut small, mut large) = (std::time::Duration::MAX, std::time::Duration::MAX);
for _ in 0..5 {
small = small.min(run(&small_packet, n));
large = large.min(run(&large_packet, 4 * n));
}
let ratio = large.as_secs_f64() / small.as_secs_f64().max(1e-6);
assert!(ratio < 10.0, "4x the attributes took {ratio:.1}x as long ({small:?}, then {large:?})");
}