perf(query-core): Reduce observer removal overhead by scttcper · Pull Request #11214 · TanStack/query

scttcper · 2026-08-18T00:19:08Z

Removing observers currently allocates a new observer array for every unsubscribe. This removes the observer in place instead, which avoids repeated copies when lots of components share a query.

The hot case is many observers sharing one query. In a local jsdom benchmark with 10,000 disabled useQuery components on the same query:

Operation	Before	After
Change every query key	190 ms	81 ms
Unmount	163 ms	15 ms

10,000 different queries are effectively unchanged because each query only has one observer:

Operation	Before	After
Mount	65.9 ms	66.9 ms
Parent rerender	52.9 ms	54.0 ms
Unmount	8.8 ms	7.8 ms

Summary by CodeRabbit

Performance
- Reduced unnecessary observer churn when subscriptions are removed.
- Preserved existing cancellation, garbage-collection, and cache notification behavior.
Release
- Included in a patch release of the query core package.

Removing observers copied the full observer list on every unsubscribe, which got expensive when thousands of components shared a query. Splice the existing list in place instead. Co-Authored-By: Codex <noreply@openai.com>

coderabbitai · 2026-08-18T00:19:18Z

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Reviewing files that changed from the base of the PR and between 279bb55 and 3d27d3a.

📒 Files selected for processing (2)

.changeset/faster-query-observer-churn.md
packages/query-core/src/query.ts

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📝 Walkthrough

Walkthrough

removeObserver now removes matching observers in place. A patch changeset documents the @tanstack/query-core change and its reduced observer churn.

Changes

Observer removal

Layer / File(s)	Summary
In-place observer removal `packages/query-core/src/query.ts`, `.changeset/faster-query-observer-churn.md`	`removeObserver` uses `splice` to remove one matching observer. The changeset records a patch release for `@tanstack/query-core`.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk:⚪ Minimal · up to 3d27d

This localized observer-removal optimization is merge-ready after normal checks and review; no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the change and benchmarks but omits the required Changes, Checklist, and Release Impact sections and their confirmations.	Add the required template sections and confirm the contributing guide, local tests, and changeset or explain why the change is dev-only.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main performance optimization in query-core.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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nx-cloud · 2026-08-18T07:29:13Z

View your CI Pipeline Execution ↗ for commit 1c5e8bc

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☁️ Nx Cloud last updated this comment at 2026-08-18 07:37:53 UTC

pkg-pr-new · 2026-08-18T07:32:44Z

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commit: 1c5e8bc

Removing an observer in place can shift the active notification loop and skip the next observer. Iterate over a shallow copy so synchronous unsubscriptions keep the old behavior without giving up the faster removal path from #11214. Co-authored-by: Codex <noreply@openai.com>

perf(query-core): Reduce observer removal overhead
3d27d3a
Removing observers copied the full observer list on every unsubscribe, which got expensive when thousands of components shared a query. Splice the existing list in place instead. Co-Authored-By: Codex <noreply@openai.com>

scttcper marked this pull request as ready for review August 18, 2026 00:27

TkDodo approved these changes Aug 18, 2026
View reviewed changes

Merge branch 'main' into scttcper/optimize-observer-removal
1c5e8bc

TkDodo merged commit 5bb089d into TanStack:mainAug 18, 2026
9 checks passed

github-actionsBot mentioned this pull request Aug 18, 2026
ci: Version Packages #11206
Open

coderabbitaiBot mentioned this pull request Aug 19, 2026
fix(query-core): notify sibling observers when one unsubscribes during dispatch #11231
Closed

scttcper mentioned this pull request Aug 20, 2026
fix(query-core): Keep observer notifications stable #11234
Merged

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perf(query-core): Reduce observer removal overhead - #11214

perf(query-core): Reduce observer removal overhead#11214
TkDodo merged 2 commits into
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scttcper:scttcper/optimize-observer-removal

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