perf: skip per-key clone when Onyx.init() hydrates the cache

[WojtekBoman]

Details

Onyx.init() loaded the persisted database into OnyxCache through merge(), which runs fastMerge(existing, value) per key. At init time existing is always undefined, so fastMerge never actually merges anything - it just walks and deep-clones every nested object of every row for no reason. On a heavy account this clone-heavy cache-write phase was measured at ~29% of total Onyx.init() time.

Adds OnyxCache.hydrate(), a bulk-load variant used only by Onyx.init(). Values are stored by reference when safe (utils.needsNormalization() is a read-only, non-allocating check for nested null/undefined and the internal ONYX_INTERNALS__REPLACE_OBJECT_MARK). Falls back to the existing fastMerge path in two cases: the key already has a value in cache (a cross-tab sync listener can race ahead of init and write a key before hydrate() reaches it), or the value itself needs normalizing.

OnyxUtils.ts's initializeWithDefaultKeyStates() now calls cache.hydrate(allDataFromStorage) instead of cache.merge(allDataFromStorage).

merge()'s inline fastMerge options were also extracted into a shared CACHE_MERGE_OPTIONS constant used by both merge() and hydrate()'s fallback, so the cache write paths can't drift apart.

Related Issues

Expensify/App#98553

Linked E/App PR

Expensify/App#98649

Automated Tests

tests/unit/onyxCacheTest.tsx covers hydrate() directly and through Onyx.init():

• Equivalence with merge(): identical cache state on an empty cache, and when keys already hold values, across fixtures with nested nulls, nested undefined, the replace-object mark, and plain values.
• Every key is registered, including keys whose stored value is nullish.
• Values are stored by reference when no normalization is needed, and normalized when they carry nested nullish properties.
• Reference stability: a hydrated value that changes nothing keeps the existing reference.
• Init-level: collection members loaded from storage are readable through collection reads, keys written while storage was still being read are merged rather than overwritten, and the resulting cache matches a merge-based init.

Manual Tests

1. Sign in to an account with a reasonably large Onyx database (many reports/reportActions), force-quit and cold-start the app.
   Verify that the app boots normally, the LHN and reports render with the same data as before the change, and no console errors appear.
2. Cold-start the app, open a report with actions containing deleted/optimistic-cleared fields (values that were null on disk).
   Verify that the report renders correctly with those fields absent, matching pre-change behavior.
3. On web, open the app in two browser tabs signed into the same account. In tab A, trigger a write (e.g. send a message) right as tab B is cold-starting/reloading.
   Verify that tab B's cache ends up consistent with tab A's write - i.e. the value isn't clobbered by hydrate()'s bulk load racing the cross-tab sync listener.

Offline tests

1. Put the device in airplane mode, force-quit and cold-start the app.
   Verify that the app boots with the last-persisted cache (same as before this change) and no data is lost or duplicated.
2. While offline, open a report and confirm previously-persisted reportActions/transactions render correctly, then go back online and verify no reconciliation errors occur.

QA Steps

Same as tests.

Author Checklist

• I linked the correct issue in the ### Related Issues section above
• I linked the corresponding Expensify/App PR in the ### Linked E/App PR section above, and verified this change against it (E/App CI passed and manual testing completed)
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android / native
  • Android / Chrome
  • iOS / native
  • iOS / Safari
  • MacOS / Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick)
  • I verified that the left part of a conditional rendering a React component is a boolean and NOT a string, e.g. myBool && <MyComponent />.
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.js or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
• If a new component is created I verified that:
  • A similar component doesn't exist in the codebase
  • All props are defined accurately and each prop has a /** comment above it */
  • The file is named correctly
  • The component has a clear name that is non-ambiguous and the purpose of the component can be inferred from the name alone
  • The only data being stored in the state is data necessary for rendering and nothing else
  • If we are not using the full Onyx data that we loaded, I've added the proper selector in order to ensure the component only re-renders when the data it is using changes
  • For Class Components, any internal methods passed to components event handlers are bound to this properly so there are no scoping issues (i.e. for onClick={this.submit} the method this.submit should be bound to this in the constructor)
  • Any internal methods bound to this are necessary to be bound (i.e. avoid this.submit = this.submit.bind(this); if this.submit is never passed to a component event handler like onClick)
  • All JSX used for rendering exists in the render method
  • The component has the minimum amount of code necessary for its purpose, and it is broken down into smaller components in order to separate concerns and functions
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.
• I have checked off every checkbox in the PR author checklist, including those that don't apply to this PR.

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-08-14.at.15.07.49.mov

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[WojtekBoman]

I have read the CLA Document and I hereby sign the CLA

[collectioneur]

LGTM! 🚀

[mkhutornyi]

NAB comments:

[mkhutornyi]

Regression test cases

1. Cold start with existing data (the main path)

1. Sign in and let the app fully load (open a few chats, a workspace, and Search).
2. Force-quit the app (swipe away on mobile, close the tab/browser on web).
3. Relaunch.
4. Verify the LHN renders the same report list as before the restart, in the same order.
5. Open a report that was open before — verify all messages, avatars, and unread indicators are identical.
6. Open Settings → Workspaces — verify categories, tags, and members are present.
7. Verify no "empty state" or skeleton flashes and then fills in for data that was already on disk.

Why: cache.hydrate() replaces setAllKeys() + cache.merge() for the entire eager load. A key registration failure shows up here as missing LHN rows or an empty workspace list.

2. Collections render fully

1. From the cold-start state above, verify the LHN report list, the workspace member list, and a report's transaction list all show every row.
2. Pull to refresh / navigate away and back — verify nothing appears or disappears.

Why: hydrate() now registers collection member keys via addKey() and marks collections dirty itself. A miss here means a collection snapshot is built from an incomplete index — the symptom is some members rendering, not zero.

3. Values with removed properties survive the restart

1. Set a workspace description, then clear it. Do the same for an optional profile field (e.g. pronouns).
2. Force-quit and relaunch.
3. Verify the cleared fields are still empty and no null leaks into the UI as the literal string "null" or a blank row that shouldn't exist.

Why: hydrate() skips normalization entirely for values that pass needsNormalization(), and only deep-cleans the ones that don't. This is the scenario where a value carrying nested nulls is stored raw.

4. Offline data after restart

1. Create an expense, then go offline before it finishes syncing.
2. Force-quit and relaunch while still offline.
3. Verify the pending expense is still visible with its offline styling.
4. Go back online — verify it syncs and the pending styling clears.

Why: exercises hydrate against optimistic data written by the previous session, including pendingAction fields.

5. Multi-tab race (web only — highest-risk scenario)

1. Open the app in two browser tabs and let both load.
2. In Tab A, send a message in a chat.
3. Immediately hard-refresh Tab B (Cmd+Shift+R) so its startup storage read overlaps the cross-tab broadcast.
4. Verify Tab B shows the new message and the chat is in the right LHN position.
5. Repeat 3–4 times — the timing window is narrow.
6. Now the inverse: in Tab A delete a message, and immediately hard-refresh Tab B.
7. Verify the deleted message does not reappear in Tab B.

Why: the existing !== undefined fallback inside hydrate() exists specifically for this race. Steps 6–7 cover a known pre-existing gap — if the deleted message does briefly reappear, that reproduces on main too and is not caused by this PR. Worth capturing on video either way.

6. Fresh install / empty storage

1. Uninstall (or clear site data) and reinstall.
2. Launch before signing in — verify the sign-in page renders normally, no crash, no hang on the splash screen.
3. Sign in and verify normal loading.

Why: hydrate({}) on an empty payload no longer resets the key index. Confirms nothing depends on that reset.

7. Sign out / sign in / switch accounts

1. Sign out, then sign in as a different account.
2. Verify none of the previous account's chats, workspaces, or avatars appear.
3. Force-quit and relaunch — verify still clean.

Why: Onyx.clear() interacts with the key index, and the index is no longer replaced wholesale at init.

8. Performance verification (this is the PR's actual goal)

1. On a release build with a large account (many reports/transactions), measure time from launch to first LHN paint.
2. Compare against a build on main with the same account and the same storage state — run each 5 times and take the median.
3. Verify the branch is not slower; a measurable improvement on large accounts is the expected result.

A Sentry span or a console.time around Onyx.init()'s resolution both work; use whichever the perf setup already tracks.

Platforms

Run 1–4 and 6–7 on iOS, Android, and web (different storage providers: SQLite vs IndexedDB, and only SQLite batches the whole table through one JSON.parse). Scenario 5 is web only. Scenario 8 on iOS and Android release builds.

[roryabraham]

Code LGTM but we should link an App PR to help the Onyx merge queue go smoother.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Can't wait for the next one!

Reviewed commit: 25cf1cb277

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[mkhutornyi]

Reviewer Checklist

• I have verified the author checklist is complete (all boxes are checked off).
• I verified the correct issue is linked in the ### Fixed Issues section above
• I verified testing steps are clear and they cover the changes made in this PR
  • I verified the steps for local testing are in the Tests section
  • I verified the steps for Staging and/or Production testing are in the QA steps section
  • I verified the steps cover any possible failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
• I checked that screenshots or videos are included for tests on all platforms
• I included screenshots or videos for tests on all platforms
• I verified that the composer does not automatically focus or open the keyboard on mobile unless explicitly intended. This includes checking that returning the app from the background does not unexpectedly open the keyboard.
• I verified tests pass on all platforms & I tested again on:
  • Android: HybridApp
  • Android: mWeb Chrome
  • iOS: HybridApp
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• If there are any errors in the console that are unrelated to this PR, I either fixed them (preferred) or linked to where I reported them in Slack
• I verified proper code patterns were followed (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick).
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I verified that this PR follows the guidelines as stated in the Review Guidelines
• I verified other components that can be impacted by these changes have been tested, and I retested again (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar have been tested & I retested again)
• If a new component is created I verified that:
  • A similar component doesn't exist in the codebase
  • All props are defined accurately and each prop has a /** comment above it */
  • The file is named correctly
  • The component has a clear name that is non-ambiguous and the purpose of the component can be inferred from the name alone
  • The only data being stored in the state is data necessary for rendering and nothing else
  • For Class Components, any internal methods passed to components event handlers are bound to this properly so there are no scoping issues (i.e. for onClick={this.submit} the method this.submit should be bound to this in the constructor)
  • Any internal methods bound to this are necessary to be bound (i.e. avoid this.submit = this.submit.bind(this); if this.submit is never passed to a component event handler like onClick)
  • All JSX used for rendering exists in the render method
  • The component has the minimum amount of code necessary for its purpose, and it is broken down into smaller components in order to separate concerns and functions
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG)
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
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  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• For any bug fix or new feature in this PR, I verified that sufficient unit tests are included to prevent regressions in this flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.
• I have checked off every checkbox in the PR reviewer checklist, including those that don't apply to this PR.

Screenshots/Videos

Android: HybridApp

Android: mWeb Chrome

iOS: HybridApp

mobile.mov

iOS: mWeb Safari

MacOS: Chrome / Safari

web.mov

[mkhutornyi]

Code LGTM but we should link an App PR to help the Onyx merge queue go smoother.

App PR is here - Expensify/App#98649

[WojtekBoman]

@roryabraham @mkhutornyi
Comments have been addressed and I’ve added a link to the App PR in the description :)

[mountiny]

code looks good, waiting for @fabioh8010 review too

[mountiny]

Checking internally the CLA action is failing due to new org wide rule

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: d1f9732745

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[chatgpt-codex-connector]

Ignore inherited properties when hydrating cache batches

When storage contains a key named __proto__ with an object value, the assignment in initializeWithDefaultKeyStates() changes allDataFromStorage's prototype; this unguarded for...in then treats every enumerable property of that stored value as a separate Onyx key and registers/caches data that does not exist under those keys. The previous Object.entries() path only processed own properties, so guard the loop with Object.hasOwn(data, key) (and likewise for the matching loop in merge()).

Useful? React with 👍 / 👎.

[WojtekBoman]

The mechanism is correct, but I don't think the guard is necessary here, and it was intentionally removed in review #821 (comment)

[fabioh8010]

Yeah I dont think this kind of situation would ever happen

[mountiny]

Thanks for the thorough review, I think we can move this ahead now

[os-botify]

🚀 Published to npm in 3.0.101 🎉