Remove Inbox from preloaded navigators to prevent CPU spike on web by TMisiukiewicz · Pull Request #84025 · Expensify/App

TMisiukiewicz · 2026-03-03T11:55:04Z

Explanation of Change

When a user with many reports opens the web app on a tab other than Inbox (e.g. Workspaces or Settings), the preloading system was mounting ReportsSplitNavigator (the Inbox navigator) in the background. This triggered a full render of the LHN with all Onyx-connected report rows, causing CPU to spike to 100% for 15–20 seconds on accounts with large report lists.

The fix is straightforward: remove NAVIGATION_TABS.INBOX from TABS_TO_PRELOAD in usePreloadFullScreenNavigators.ts. The Inbox tab doesn't need to be preloaded — it's the default tab and will mount naturally when navigated to. The remaining preloaded tabs (Workspaces and Settings) are lightweight by comparison and don't trigger the same expensive LHN render.

Fixed Issues

$ #80560
PROPOSAL:

Tests

Web only

Open the app
Navigate to inbox
Navigate to other tabs
Verify navigating works fine

Verify that no errors appear in the JS console

Offline tests

N/A

QA Steps

Same as tests

Verify that no errors appear in the JS console

PR Author Checklist

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

web-preload.mov

codecov · 2026-03-03T12:03:25Z

Codecov Report

✅ Changes either increased or maintained existing code coverage, great job!

Files with missing lines	Coverage Δ
...ion/AppNavigator/usePreloadFullScreenNavigators.ts	`14.28% <100.00%> (ø)`
... and 16 files with indirect coverage changes

…m-preloaded-screens

melvin-bot · 2026-03-03T14:24:19Z

@hungvu193 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]

hungvu193 · 2026-03-03T16:33:32Z

src/libs/Navigation/AppNavigator/usePreloadFullScreenNavigators.ts


 // Currently the Inbox, Workspaces and Account tabs are preloaded, while Search is not preloaded due to its potential complexity.
-const TABS_TO_PRELOAD = [NAVIGATION_TABS.INBOX, NAVIGATION_TABS.WORKSPACES, NAVIGATION_TABS.SETTINGS];
+const TABS_TO_PRELOAD = [NAVIGATION_TABS.WORKSPACES, NAVIGATION_TABS.SETTINGS];


I can see CPU usage deceases significantly, so 💯 to this change.

But since the most heavy tab is removed from preload tab, I wonder if we really need to preload WORKSPACES and SETTINGS tabs since they're lightweight and most of their data needed for displaying the UI of these two page come from OpenApp.

I tried to remove usePreloadFullScreenNavigators and I don't see different while switching between these tab. Do you have any metric for the usePreloadFullScreenNavigators? And what kind of data did you measured?

@hungvu193 while I do not see much difference on Web, I can see preloading of Workspaces and Setting screens bringing good results on mobile - results when navigating from Home to Workspaces on iOS without preloading:

🔴 Duration Diff: 680.679 ms (+332.8%) 🔴 Commit Count Diff: 12

@TMisiukiewicz Do you think we still need this preload logic on web at all?

@hungvu193 please check this comment. I believe keeping the preloading on web makes sense for both Settings and Workspaces

mountiny · 2026-03-03T21:38:25Z

When the preloading has been implemented it did help with performance @sumo-slonik @WojtekBoman, how come that now its showing as the reverse helps as well?

…m-preloaded-screens

WojtekBoman · 2026-03-04T10:51:00Z

Hi, I’d like to share my thoughts on the preload topic.

Regarding the Settings and Workspace tabs, they do indeed run faster. Currently on web this is only noticeable during the first navigation because it has been disabled in this PR: #83887. Personally, I think we should remove this check if we want to disable preloading the Inbox tab; since these screens are light, there’s no reason not to preload them if it provides a performance gain. Because of that PR, we aren't preloading these screens when they are in the navigation state, which might be why the improvement isn't currently visible after first navigation to these screens.

To show it, I recorded a video comparing the version with and without preload. To further illustrate it, I preloaded Home tab along with Settings and Account tabs and showed times when switching between them. As you can see on the video, with preloading we reach times below 100ms where without this mechanism these times are much higher than this value (approximately 2 times slower without preloading).

As for the Inbox, I agree we should disable it temporarily to prevent CPU spikes. Loading data from the OpenReport API command in the background is heavy and we need to consider how to optimize it and integrate it with the preload mechanism. In the meantime, @sumo-slonik and I will investigate this further, we are currently working on reusing the navigator keys responsible for rendering tabs here.

When the preloading has been implemented it did help with performance @sumo-slonik @WojtekBoman, how come that now its showing as the reverse helps as well?

Answering your question @mountiny, I think it's worth using this mechanism, but we need to reconsider how to optimize it in specific cases, maybe it's worth calling OpenReport when we're already navigating instead of doing it in the background.

Finally, I would opt for:

Temporarily disabling the inbox tab preloading.
Reverting the changes made to usePreloadFullScreenNavigators in that PR so we don't block the preloading of other navigators.

Screen.Recording.2026-03-04.at.08.53.35.mov

JmillsExpensify

No product review required.

TMisiukiewicz · 2026-03-04T12:37:43Z

@WojtekBoman thanks your your input! Let's do it suggested way - I'll revert it once we get this one merged and deployed to avoid the possibility of a temporary regression in between

sumo-slonik · 2026-03-04T14:40:47Z

Preload Analysis – iOS Navigation Performance

I have thoroughly verified the preload behavior across all navigation transitions on iOS. I am currently collecting profiler traces for the web version and will share the results in a separate message.

Key Observation

The main issue appears to be JavaScript thread overload during heavy operations (e.g., screen unmounting). In such cases, preload itself may block the JS thread, which negatively impacts performance.

We should analyze when preload is triggered and ensure it runs only when the main thread has enough available capacity to handle it.

Performance Results

Below are the averages from 5 measurements per transition, comparing preload enabled vs. disabled.

1. Navigation to Home

Transition	Effect of Preload
Inbox → Home	30.5% faster
Reports → Home	238% slower
Workspaces → Home	160% slower
Accounts → Home	23% faster

2. Navigation to Workspaces

Transition	Effect of Preload
Reports → Workspaces	6.7% faster
Home → Workspaces	61% faster
Accounts → Workspaces	53% faster
Inbox → Workspaces	75% faster

3. Navigation to Account

Transition	Effect of Preload
Reports → Accounts	90.1% slower
Inbox → Accounts	60.1% faster
Home → Accounts	27.4% faster
Workspaces → Accounts	62.5% slower

I agree that until we improve the preload logic, we can temporarily disable preload for the Inbox. However, I would keep preload enabled for the Settings and Workspaces tabs, as their preloading is not as resource-intensive.

Additionally, I suggest adding preload for the Home tab once we resolve the current JavaScript thread overload issues. After that, we should also revisit the Inbox preload and explore whether it can be made lighter — for example, by preloading only empty navigators instead of full screen content.

Combined with a key reuse–based approach, preload could potentially be triggered only once per tab. After the initial preload, we would reuse the existing navigator key, eliminating the need for repeated preload executions for the same tab.

Conclusions

Performance degradation occurs primarily when navigating away from Workspaces and Reports. This is where we should focus optimization efforts.

In most other scenarios, preload provides significant performance gains. When this solution was originally implemented, it clearly improved performance, so something must have changed later that introduced the regression.

Recommendation

Temporarily disable preload for Inbox
Keep preload enabled for Accounts and Workspaces
Research smarter preload triggering (only when the main thread is idle or has available capacity) and investigate a lighter preload strategy for Inbox (e.g., preloading empty navigators only)

hungvu193 · 2026-03-04T15:23:21Z

Thanks for the insight @sumo-slonik 🙏 . I'll go ahead and approve so we can move forward to the next part.

hungvu193 · 2026-03-04T15:23:32Z

Reviewer Checklist

I have verified the author checklist is complete (all boxes are checked off).
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Screenshots/Videos

Android: HybridApp

Android: mWeb Chrome

iOS: HybridApp

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-03-03.at.21.35.02.mov

sumo-slonik · 2026-03-04T16:34:56Z

Web – Preload Conclusions

Despite its drawbacks, based on the tests @jakubstec and I conducted, preload provides a some performance gain on Web, and in my opinion we should continue using it.

Below are the average results (preload enabled vs. disabled):

1. Navigation to Home

Transition	Effect of Preload
Inbox → Home	2% slower
Reports → Home	56.0% faster
Workspaces → Home	35.4% slower
Accounts → Home	92.5% slower

2. Navigation to Workspaces

Transition	Effect of Preload
Home → Workspaces	42.0% faster
Inbox → Workspaces	25.2% faster
Reports → Workspaces	49.8% faster
Accounts → Workspaces	57.5% faster

3. Navigation to tAccounts

Transition	Effect of Preload
Home → Accounts	8.0% faster
Inbox → Accounts	22.4% faster
Reports → Accounts	47.4% faster
Workspaces → Accounts	88.1% slower

Summary

Because of this overall positive impact, I believe we should keep preload enabled on Web.

At the same time, it’s important to acknowledge that preload has both advantages and drawbacks. The data clearly shows that while we gain improvements in many scenarios, there are also measurable regressions in specific transitions. The goal is not to present preload as universally beneficial, but rather to optimize how and when it runs.

As the second part of my key reuse–based solution, I will ensure that preload is executed only once per tab, as mentioned earlier. With key reuse in place, we aim to:

Avoid repeated preload executions for the same screen
Reduce unnecessary JS workload
Better control when heavy initialization happens
Preserve the measurable gains we’re seeing today

Preload is not perfect in its current form, but with the improvements discussed (smarter triggering + key reuse), it should provide more consistent benefits and reduce the existing regressions. Overall, after these adjustments, the expected balance should be clearly more positive.

mountiny

Sounds like we agree to remove it for Inbox for now and explore improvements later

github-actions · 2026-03-04T22:26:44Z

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

github-actions · 2026-03-04T22:32:00Z

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OSBotify · 2026-03-04T22:52:38Z

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

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🚀 Deployed to staging by https://github.com/mountiny in version: 9.3.32-0 🚀

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melvin-bot bot assigned TMisiukiewicz Mar 3, 2026

TMisiukiewicz changed the title ~~[No QA] Remove Inbox from preloaded navigators to prevent CPU spike on web~~ Remove Inbox from preloaded navigators to prevent CPU spike on web Mar 3, 2026

remove Inbox from preloaded screens

3c3bf8e

TMisiukiewicz force-pushed the perf/remove-inbox-from-preloaded-screens branch from 5ebaf1f to 3c3bf8e Compare March 3, 2026 13:03

Merge remote-tracking branch 'origin/main' into perf/remove-inbox-fro…

9e41c1a

…m-preloaded-screens

TMisiukiewicz marked this pull request as ready for review March 3, 2026 14:24

TMisiukiewicz requested review from a team as code owners March 3, 2026 14:24

melvin-bot bot requested review from JmillsExpensify and hungvu193 and removed request for a team March 3, 2026 14:24

melvin-bot bot removed the request for review from a team March 3, 2026 14:24

TMisiukiewicz mentioned this pull request Mar 3, 2026

[Tracking] Large customer account performance and UX support #80560

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hungvu193 reviewed Mar 3, 2026

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TMisiukiewicz added 2 commits March 4, 2026 08:42

Merge remote-tracking branch 'origin/main' into perf/remove-inbox-fro…

a889052

…m-preloaded-screens

update comment

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JmillsExpensify reviewed Mar 4, 2026

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hungvu193 approved these changes Mar 4, 2026

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mountiny merged commit 39c4289 into Expensify:main Mar 4, 2026
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github-actions bot mentioned this pull request Mar 4, 2026

Investigate workflow job failing on main: typecheck / typecheck #84204

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TMisiukiewicz mentioned this pull request Mar 5, 2026

[CP Staging][No QA] Revert "Prevent LHN from remounting after navigating away from Inbox" #84249

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mkhutornyi mentioned this pull request Mar 5, 2026

Accounting - Central pane shows Workspaces page when Accounting page is loading #84225

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Deploy Checklist: New Expensify 2026-03-06 #84352

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Explanation of Change

Fixed Issues

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sumo-slonik commented Mar 4, 2026

Preload Analysis – iOS Navigation Performance

Key Observation

Performance Results

1. Navigation to Home

2. Navigation to Workspaces

3. Navigation to Account

Conclusions

Recommendation

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sumo-slonik commented Mar 4, 2026

Web – Preload Conclusions

1. Navigation to Home

2. Navigation to Workspaces

3. Navigation to tAccounts

Summary

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