Long documents slow Chrome/Chromium to a halt

[netzpolitikorg]

While longer markdown documents are not super fast in any browser, there seems to be an overlap of performance-eating bugs or circumstances when opening long (>1000 lines) markdown files.

To Reproduce
Steps to reproduce the behavior:

1. Create a files with a variety of headlines, plain-text, and lists with sub-lists that is at least 10000 lines long. It doesn't have to be particular complicated, but long.
2. Open it in Chromium.
3. Wait a long time for it to render at all.
4. Wait a few seconds every time you try to scroll or edit the document.

Expected behavior
A maybe slow, but not unusable document.

Server details:

• Nextcloud version: 29.0.0.19 and 29.0.1 RC1
• PHP Version: 8.2
• Database: PostgreSQL 15.6
• Text app version: 3.10.0

Client details:

• OS: various Linuxes (Ubuntu, Arch, Debian)
• Browser: Chromium
• Browser version: 125, 126, and others
• Device: various laptops

Logs

Nextcloud log (data/nextcloud.log)

No related server-side logs. This issue appears to be entirely client-side.

Browser log

Console and Network tab are pretty quiet, but the Performance tab shows a lot of activity. We can provide the corresponding json file if this issue can't be reproduced by anyone else.

[mejo-]

If this only happens in Chromium (not Firefox), maybe it's related to nextcloud/server#44122, which hopefully will be fixed soon (there's already PRs in review to fix it).

[netzpolitikorg]

Ok. We don't use the dashboard, but we're happy to wait and test after the PR is released 💚

[max-nextcloud]

I just tried to reproduce this copying the longest good wikipedia article into a text document. It showed a number of issues:

• Editing in firefox still works but file won't be saved.
• Read only share does not open the file content.
• Transferred data is fairly large - 3.5MB step for a 0.5 MB article according to Wikipedias own measurement

edit: Some of this is probably due to inconsistencies in data format. For example it looks like we expect our images to have some alt attribute but the pasted ones do not have any:

[helmo]

I'm also seeing slowdowns in Chrome, while Firefox works fine.
The markdown filesize is about 180kb. I've mitigated it for now by splitting it into multiple files.

This is on nextcloud 29.0.7

This issue seems related to #908