Optimize schema-comparator diffing performance#94
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…schemas) Key optimizations: - Eliminate intermediate Vec allocations via diff_into(&mut Vec) pattern - Single-pass field matching: merge removals + common diffs into one iteration - Unified diff_directives_into replacing 3 separate directive functions - Ptr equality fast path for identical schemas (0µs) - HashMap fallback for types with 64+ fields (O(1) lookups on large types) - CriticalityLevel enum to avoid Cow string allocations during sorting - Early exits for empty directives/arguments, #[inline] hints on hot paths - Pre-allocate changes Vec with capacity 256 - Criterion benchmark suite with real schema fixtures Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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adampetro
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Mar 19, 2026
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| let src = std::fs::read_to_string(data_path(name)).unwrap(); | ||
| let doc: DefinitionDocument = DefinitionDocument::parse(Box::leak(src.into_boxed_str())) | ||
| .result | ||
| .expect("Schema had parse errors"); | ||
| let leaked = Box::leak(Box::new(doc)); |
Contributor
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Could we use include_str! to avoid some of the leaking? Or would that slow down compiles a lot?
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| fn compare_with_changes(c: &mut Criterion) { | ||
| c.bench_function("docs schema vs itself (no changes)", |b| { | ||
| b.iter(|| compare(&*DOCS_SCHEMA, &*DOCS_SCHEMA)); | ||
| }); |
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I'm a bit confused because it's called compare_with_changes but then the first one has no changes?
| ); | ||
| } | ||
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| #[cold] |
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| changes.extend( | ||
| directive_additions::<S, _>(self.old_type_definition, self.new_type_definition).map( | ||
| |directive| Change::DirectiveAdded { | ||
| directive, | ||
| location: DirectiveLocation::InputFieldDefinition, | ||
| member_name: self.old_field_definition.name(), | ||
| }, | ||
| ), | ||
| ); | ||
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| changes.extend( | ||
| directive_removals::<S, _>(self.old_type_definition, self.new_type_definition).map( | ||
| |directive| Change::DirectiveRemoved { | ||
| directive, | ||
| location: DirectiveLocation::InputFieldDefinition, | ||
| member_name: self.old_field_definition.name(), | ||
| }, | ||
| ), | ||
| ); |
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| // Fast path: if both schemas are the same object, there are no changes | ||
| if std::ptr::eq(self.old_schema_definition, self.new_schema_definition) { | ||
| return Vec::new(); | ||
| } |
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will this ever be useful in practice?
| }), | ||
| ); | ||
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| // Schema-level directive removals |
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are we missing directive diffs?
| directive_definition: _, | ||
| argument_definition, | ||
| } => { | ||
| if argument_definition.is_required() { |
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should we be checking for a default value?
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Optimize schema-comparator diffing performance (~65% faster on large schemas)
Key optimizations:
Note: this is a manually curated (with the help of Claude) and cleaned up version of an
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