Coalesce OnyxDerived recomputations via macrotask scheduling by fabioh8010 · Pull Request #95287 · Expensify/App

fabioh8010 · 2026-07-03T14:35:05Z

Explanation of Change

Slack proposal: https://expensify.slack.com/archives/C08CZDJFJ77/p1783094934084619?thread_ts=1782801937.464879&cid=C08CZDJFJ77

OnyxDerived values (e.g. reportAttributes) open one Onyx connection per dependency, and each connection callback recomputes the derived value synchronously. Because Onyx delivers a single logical write (a server response touching reports + transactions + violations + report actions, etc.) as several separate broadcasts, one logical update recomputes each derived value many times back-to-back, blocking the JS thread during startup and report opens. reportAttributes alone has 13 dependencies and is one of the heaviest computes in the app.

This PR coalesces the per-dependency recomputes for each derived value into a single compute per logical update.

How it works

Coalescing. recomputeDerivedValue no longer computes inline — it records the triggering dependency in a pending set and, if no flush is already scheduled, schedules one on the next macrotask. Every dependency callback from the same logical update lands in that one pending flush, so N recomputes collapse to 1.
Flush-time delta reconstruction. Instead of relying on Onyx's per-broadcast sourceValue (which doesn't survive coalescing — you'd be merging N partial payloads — and is being phased out), the flush reconstructs the changed-member delta itself: for each collection dependency that fired, it diffs the current snapshot against a baseline captured at the previous flush, via a new shared getCollectionDelta helper. Onyx's structural sharing keeps unchanged members reference-equal, so this is a cheap reference scan. The first flush has no baselines, so it computes from scratch and captures baselines for subsequent diffs.
scheduleMacrotask (MessageChannel). The flush is scheduled with a small scheduleMacrotask helper that uses MessageChannel on web — the same technique React's scheduler uses — because setTimeout is throttled in background tabs (rules varies through different browsers) and clamped to 4ms after nested calls. It falls back to setTimeout on React Native (no MessageChannel; the JS thread is fully suspended in the background there anyway) and in tests.
Incremental configs hardened to honor every coalesced trigger. Configs that update incrementally previously assumed a single triggering dependency per compute. Coalescing can now deliver several changed dependencies in one compute, so any config that branched on "which one changed" was updated to process all of them:
- reportAttributes — its personal-details fast-path short-circuits only when personal details are the sole trigger.
- reportTransactionsAndViolations — processes the union of transactions that changed directly and transactions whose violations changed (was an if/else that dropped the second trigger).
- sortedReportActions — takes its report-actions incremental path only when report actions are the sole trigger; a batched REPORT change falls back to a full recompute.

With recomputes coalesced, one logical update produces exactly one compute of each derived value instead of one-per-dependency. Derived values become eventually consistent within one macrotask of the originating write; consumers re-render normally through useOnyx when the single updated value lands.

Fixed Issues

$ #95301
PROPOSAL:

Tests

Pin/Unpin two reports in LHN, assert they were pinned/unpinned and LHN was re-ordered correctly.
Draft a message to two reports in LHN, assert they were marked and LHN was re-ordered correctly.
Mark two reports in LHN as read/unread, assert they were marked/unmarked, the Unread count indicator changed and LHN was re-ordered correctly.
From another user send a expense to this one, mark it as paid, assert it appeared correctly and the To-dos count indicator changed.
Send a message to a user you never sent before, assert it appeared in LHN.
Delete that message, assert the chat disappeared from LHN.

MessageChannel testing (web-only)

I'm using Firefox as it's easier to demonstrate the differences in the latencies when comparing with setTimeout.

Before testing, apply these changes to src/libs/actions/OnyxDerived/index.ts:

diff --git a/src/libs/actions/OnyxDerived/index.ts b/src/libs/actions/OnyxDerived/index.ts
index 0413646e141..2e933211b32 100644
--- a/src/libs/actions/OnyxDerived/index.ts
+++ b/src/libs/actions/OnyxDerived/index.ts
@@ -71,6 +71,8 @@ function init() {
 
             // Coalesce per-dependency recomputes from one logical change into a single compute on the next macrotask.
             let flushScheduled = false;
+            // TEMP [perf] timestamp captured when a flush is scheduled, to measure schedule -> flush latency.
+            let scheduledAt = 0;
             // Dependency indexes that fired since the last flush; their deltas are reconstructed at flush time.
             const pendingDependencyIndexes = new Set<number>();
             // Snapshot of each collection dependency captured at the last flush. We diff the current snapshot
@@ -109,6 +111,13 @@ function init() {
             const flushRecompute = () => {
                 flushScheduled = false;
 
+                // TEMP [perf] measure how long the scheduled macrotask actually took to run (schedule -> flush).
+                // In a backgrounded web tab, setTimeout is throttled (~1s+) while MessageChannel is not.
+                const flushLatency = Math.round(performance.now() - scheduledAt);
+                const tabHidden = typeof document !== 'undefined' && document.visibilityState === 'hidden';
+                // eslint-disable-next-line no-console
+                console.log(`[perf][OnyxDerived] ${key} flush latency ${flushLatency}ms${tabHidden ? ' (tab hidden)' : ''}`);
+
                 // Reconstruct the source values at flush time by diffing each dependency that fired since the
                 // last flush against its last-flushed snapshot. On the very first flush we have no baselines, so
                 // we compute from scratch (undefined sourceValues) and capture snapshots for future diffs.
@@ -168,6 +177,8 @@ function init() {
                     return;
                 }
                 flushScheduled = true;
+                // TEMP [perf] stamp the schedule time so flushRecompute can log schedule -> flush latency.
+                scheduledAt = performance.now();
                 scheduleMacrotask(flushRecompute);
             };

With an logged in account, duplicate the current Tab and wait for them to stop processing.
In Tab A, execute the following command in the console: await Onyx.merge('session', {email: 'test@email.com'});.
Go to Tab B and check [perf][OnyxDerived] logs. Assert the flush latency is lesser than 1000 ms.

If you change scheduleMacrotask.ts to always use the setTimeout fallback, the flush latency will be greater than 1000 ms.

Verify that no errors appear in the JS console

Offline tests

N/A

QA Steps

Same as Tests, except MessageChannel testing (web-only).

Verify that no errors appear in the JS console

PR Author Checklist

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

Screen.Recording.2026-07-06.at.10.38.55.mov

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-07-06.at.10.32.24.mov

MessageChannel testing (web-only)

Screen.Recording.2026-07-06.at.10.21.14.mov

…otask-scheduling

fabioh8010 · 2026-07-03T14:36:39Z

This change is needed because of getCollectionDelta, it was the same change I applied in 076914f in #93438

fabioh8010 · 2026-07-03T15:02:30Z

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chatgpt-codex-connector · 2026-07-03T15:07:36Z

+                }
+
+                pendingDependencyIndexes.clear();
+                runCompute(sourceValues);


Preserve secondary triggers in coalesced recomputes

When this flush passes all pending dependency changes to a config at once, several existing incremental configs still assume only one source key is present. For example, reportTransactionsAndViolations.compute uses if (transactionsUpdates) ... else if (transactionViolationsUpdates) ..., so a single Onyx.update that changes transaction A and violations for transaction B now only processes A; before this change the callbacks ran separately and B's violation map was updated. The same pattern exists in sortedReportActions when REPORT_ACTIONS is batched with REPORT/NETWORK, so coalescing needs to either force a full recompute for mixed triggers or update those configs to handle all triggers together.

Useful? React with 👍 / 👎.

Good catch, fixed in 0842b78.

However I'm not implementing the general suggested fix (full recompute on any mixed trigger) because that would defeat the goal of this PR, so I'm instead fixing reportTransactionsAndViolations and sortedReportActions to account for this scenario. The other derived files were checked and they are already safe.

codecov · 2026-07-03T15:10:51Z

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
...bs/actions/OnyxDerived/configs/reportAttributes.ts	`95.67% <100.00%> (-2.16%)`	⬇️
...Derived/configs/reportTransactionsAndViolations.ts	`100.00% <100.00%> (ø)`
...actions/OnyxDerived/configs/sortedReportActions.ts	`94.73% <100.00%> (+0.09%)`	⬆️
src/libs/actions/OnyxDerived/index.ts	`98.21% <100.00%> (+1.19%)`	⬆️
src/libs/actions/OnyxDerived/utils.ts	`100.00% <100.00%> (ø)`
src/libs/getCollectionDelta.ts	`100.00% <100.00%> (ø)`
src/libs/scheduleMacrotask.ts	`100.00% <100.00%> (ø)`
...ctions/OnyxDerived/configs/visibleReportActions.ts	`96.42% <94.44%> (+1.60%)`	⬆️
... and 21 files with indirect coverage changes

…& sortedReportActions recomputes

melvin-bot · 2026-07-06T10:00:06Z

@shubham1206agra Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

OSBotify · 2026-07-08T16:58:15Z

✋ This PR was not deployed to staging yet because QA is ongoing. It will be automatically deployed to staging after the next production release.

github-actions · 2026-07-08T17:33:07Z

🚧 roryabraham has triggered a test Expensify/App build. You can view the workflow run here.

github-actions · 2026-07-08T17:42:16Z

🧪🧪 Use the links below to test this adhoc build on Android, iOS, and Web. Happy testing! 🧪🧪
Built from App PR #95287.

Android 🤖	iOS 🍎
https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-android-Adhoc-790fafb8ae9-706a9bc-58bace2e8157d984bf483b2c36acb8e0f02f264b/index.html	https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-ios-device-AdHoc-790fafb-706a9bc-631b8f40657b27ed3b062857c68c5b9d03bd8b5a/index.html

Web 🕸️
https://95287.pr-testing.expensify.com

👀 View the workflow run that generated this build 👀

OSBotify · 2026-07-09T11:06:05Z

🚀 Deployed to staging by https://github.com/roryabraham in version: 9.4.32-0 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅

MelvinBot · 2026-07-09T11:07:52Z

🤖 I reviewed the changes in this PR to determine whether any Expensify help site articles under docs/articles need updating.

No help site changes are required.

This PR is a purely internal performance optimization — it coalesces per-dependency OnyxDerived recomputations into a single compute per logical update via macrotask scheduling. Every changed file is engineering-internal:

src/libs/actions/OnyxDerived/* — derived-value computation logic (reportAttributes, reportTransactionsAndViolations, sortedReportActions, visibleReportActions, index, types, utils)
src/libs/getCollectionDelta.ts, src/libs/scheduleMacrotask.ts — new internal helpers
cspell.json — spell-check dictionary entry (macrotask)
tests/** — unit/UI tests

There is no change to user-facing behavior: no new features, UI, tabs, settings, buttons, or workflows. Derived values remain eventually consistent within one macrotask of the originating write, and consumers re-render as before through useOnyx. The help site documents product features and behavior, none of which is affected here.

Because no changes are needed, I did not create a draft docs PR.

@fabioh8010, please review the linked help site PR and confirm it reflects the current behavior. Then mark the linked help site PR Ready for review

mitarachim · 2026-07-09T12:19:06Z

Deploy Blocker #95696 was identified to be related to this PR.

mitarachim · 2026-07-09T12:43:37Z

Deploy Blocker #95698 was identified to be related to this PR.

mitarachim · 2026-07-09T13:15:52Z

Deploy Blocker #95700 was identified to be related to this PR.

Reverts the coalescing engine that caused deploy blockers, scoped to just the OnyxDerived changes on top of current main. Restores the synchronous, per- dependency recompute engine (Onyx sourceValue based) and keeps waitForCollectionCallback, matching main's current Onyx 3.0.86 (the onyx-store work that removed it, #93436, was already reverted separately). Removes getCollectionDelta, scheduleMacrotask, and the triggeredKeys/flush changes. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mitarachim · 2026-07-09T16:00:35Z

Deploy Blocker #95721 was identified to be related to this PR.

jponikarchuk · 2026-07-09T19:41:26Z

Deploy Blocker #95753 was identified to be related to this PR.

OSBotify · 2026-07-10T13:43:08Z

🚀 Deployed to production by https://github.com/grgia in version: 9.4.32-3 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅

Bundle Size Analysis (Sentry):

Android

This reverts commit 4c28035.

sosek108 and others added 5 commits June 25, 2026 13:28

schedule onyx derived values as macrotask

28b09a0

Merge remote-tracking branch 'exfy/main' into perf/derived-value-macr…

127ce0b

…otask-scheduling

Merge branch 'main' into perf/derived-value-macrotask-scheduling

daac1e1

Merge branch 'main' into perf/derived-value-macrotask-scheduling

32fa2b4

temp

fceec9a

melvin-bot Bot assigned fabioh8010 Jul 3, 2026

fabioh8010 commented Jul 3, 2026

View reviewed changes

fabioh8010 added 2 commits July 3, 2026 15:44

Cleanup

1100c67

Merge branch 'main' into perf/derived-value-macrotask-scheduling-2

0ebbee3

Fix formatting

24222c6

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fabioh8010 added 4 commits July 3, 2026 16:48

fix: honor all triggers in coalesced reportTransactionsAndViolations …

0842b78

…& sortedReportActions recomputes

Implement scheduleMacrotask lib

3288505

Merge branch 'main' into perf/derived-value-macrotask-scheduling-2

2006be2

Update cspell.json

1f3ddea

fabioh8010 marked this pull request as ready for review July 6, 2026 10:00

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[Due for payment 2026-08-06] [$125] Coalesce OnyxDerived recomputes into one macrotask flush #95301

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Comment thread src/hooks/useCollectionDelta.ts Outdated

Remove useCollectionDelta

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[Due for payment 2026-09-02] [$250] Certain actions in LHN don't sync between tabs #94839

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roryabraham merged commit 790fafb into Expensify:main Jul 8, 2026
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Deploy Checklist: New Expensify 2026-07-09 #95677

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[Due for payment 2026-07-17] Chat - Chat Report appears on user's name when start new chat #95696

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[CP Staging] Revert "Coalesce OnyxDerived recomputations via macrotask scheduling" #95715

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This was referenced Jul 22, 2026

Coalesce OnyxDerived recomputations via microtask scheduling #96785

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Remove sourceValue from Onyx #93438

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Revert "Revert OnyxDerived macrotask coalescing (PR #95287)"

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This reverts commit 4c28035.

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[$250] [DEV] Expense report/thread not loading properly #96718

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Explanation of Change

How it works

Fixed Issues

Tests

MessageChannel testing (web-only)

Offline tests

QA Steps

PR Author Checklist

Screenshots/Videos

MessageChannel testing (web-only)

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