⚡ Bolt: Optimize talk grouping to prevent O(N²) allocations#222
⚡ Bolt: Optimize talk grouping to prevent O(N²) allocations#222anyulled wants to merge 1 commit into
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This commit replaces the `reduce` implementation in `groupTalksByTrack` with a single-pass `forEach` loop. By directly mutating a local `Map` and appending to existing arrays using `.push()`, we avoid the amortized O(N^2) memory allocations caused by using the array spread operator (`[...arr, item]`) and object spread operator (`...acc`) on each iteration. Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
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📝 WalkthroughWalkthrough
ChangesMap-based Track Grouping
Estimated code review effort🎯 1 (Trivial) | ⏱️ ~3 minutes Possibly related PRs
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Code Review
This pull request refactors the groupTalksByTrack function in hooks/useTalks.ts to improve performance by replacing a O(N^2) reduce implementation with a more efficient O(N) approach using a Map. Feedback suggests further optimizing the loop by using for...of instead of forEach to reduce function call overhead and improve readability.
| talks.forEach((talk) => { | ||
| const track = getTrackFromTalk(talk); | ||
| return { | ||
| ...acc, | ||
| [track]: [...(acc[track] || []), talk], | ||
| }; | ||
| }, {}); | ||
| const existing = map.get(track); | ||
| if (!existing) { | ||
| map.set(track, [talk]); | ||
| } else { | ||
| existing.push(talk); | ||
| } | ||
| }); |
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While forEach is a significant improvement over the previous for...of loop is generally preferred in performance-critical code within JavaScript engines like V8. It avoids the overhead of a function call per iteration and is often more readable for side-effect-heavy operations like populating a collection. Additionally, the logic can be slightly more concise.
| talks.forEach((talk) => { | |
| const track = getTrackFromTalk(talk); | |
| return { | |
| ...acc, | |
| [track]: [...(acc[track] || []), talk], | |
| }; | |
| }, {}); | |
| const existing = map.get(track); | |
| if (!existing) { | |
| map.set(track, [talk]); | |
| } else { | |
| existing.push(talk); | |
| } | |
| }); | |
| for (const talk of talks) { | |
| const track = getTrackFromTalk(talk); | |
| const group = map.get(track); | |
| if (group) { | |
| group.push(talk); | |
| } else { | |
| map.set(track, [talk]); | |
| } | |
| } |
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💡 What
Replaced the
reduceimplementation in thegroupTalksByTrackutility (inhooks/useTalks.ts) with aforEachloop that populates aMapdirectly. It uses.push()to append items instead of the array spread syntax[...arr, item].🎯 Why
The original implementation used object and array spread syntaxes ($O(N^2)$ memory allocations and heavy Garbage Collection overhead. The new $O(N)$ time with minimal allocations.
...accand[...existing, talk]) inside thereduceaccumulator. This is a common JavaScript anti-pattern when dealing with larger collections, as it creates a brand new array and a brand new object on every single iteration, leading toMapand.push()approach executes in strict📊 Impact
🔬 Measurement
All 137 test suites were run (including schedule and hook performance tests) and passed successfully without any visual or functional regressions. The linting rules (including strict
no-restricted-syntaxforlet) remain fully satisfied.PR created automatically by Jules for task 10532032069544085668 started by @anyulled
Summary by CodeRabbit
Note: This release contains no user-facing changes—purely internal improvements.