Add pdf to page fails with 500 on 33.0.6 (Preview error)

[Aveyron-RetD]

Describe the bug
A clear and concise description of what the bug is.

I get a display error when I insert a pdf to a page

To Reproduce
Steps to reproduce the behavior:

1. load a PDF
2. error occur

Expected behavior
This did not use to happen. With text files this works properly.

Screenshots
If applicable, add screenshots to help explain your problem.

Server details:

• Nextcloud version: 33.0.6
• PHP Version: [e.g. 8.2]
• Database: [e.g. MariaDB 10.6]

Client details:

• OS: Windows 11
• Browser: Firefox
• Browser version: [e.g. 22]
• Device: [e.g. iPhone6, desktop]

With a pdf

With a text file

Logs

Nextcloud log (data/nextcloud.log)

Insert your Nextcloud log here

Browser log

Insert your browser log here, this could for example include:

With a text file this is the request







a) The javascript console log
b) The network log
c) ...

[Aveyron-RetD]

@kumesomevosu please submit a pull request but a .exe in a zip that seems to be good way to load a virus. So no thank you !!!

[Aveyron-RetD]

Ok we solved this issue with Claude

---

n v33, the preview system was released from oc_filecache to 4 dedicated tables:

SHOW TABLES LIKE '%review%';
-- oc_preview_generation, oc_preview_locations, oc_preview_versions, oc_previews

oc_previews : a line by (file, size) — file_id, storage_id, location_id, width, height, max, cropped, etag, mtime, size.
oc_preview_locations : maps a preview to an object storage (bucket_name, object_store_name) if applicable. location_id NULL = local storage.
oc_preview_generation : asynchronous generation queue (uid, file_id, queued_at).
oc_preview_versions : tracked by file version.

4. Requests for confirmation

SELECT id, file_id, storage_id, location_id, width, height, max, cropped, mtime, size, etag
FROM oc_previews WHERE file_id IN (85251, 69874, 107944);

SELECT id, uid, file_id, queued_at FROM oc_preview_generation
WHERE file_id IN (85251, 69874, 107944);

Results :

oc_preview_generation : empty → no asynchronous generation backlog in question.
oc_previews : lines exist, with location_id = NULL (thus planned local storage, no objectstore) and complete and consistent metadata (etag, mtime, size in bytes corresponding exactly to the advertised size). The database therefore thinks that these previews exist and have a precise weight, while no file is present on the disk.
The terms of these lines are spread over several months (Nov. 2025 → June 2026) → recurring problem in time, not an isolated incident.

Cause identified

Known bug of Nextcloud 33.x: orphaned entries in oc_previews (complete metadata in base, but file never written or disappeared on the local disk), triggering a NotFoundException when playback. Preview system completely rewritten in v33 (separation from oc_filecache), so still young.

Corresponding upstream ticket, identical symptom (version 33.0.0.3) :
nextcloud/server#56485

No native occ command corrects this specific case:

sudo -u www-data php occ list | grep -i preview

preview:cleanup exists but only processes previews that have become obsolete after a change in config sizes — not orphaned lines without an associated file.
Resolution applied
Targeted patch (per file)

CREATE TABLE oc_previews_backup_YYYYMMDD AS
SELECT * FROM oc_previews WHERE file_id IN ();

DELETE FROM oc_previews WHERE file_id IN ();

sudo -u www-data php occ preview:generate -vvv

Check: the folder appears with the expected PNG file(s), size in bytes consistent with the old line DB.

Successfully applied to: 85251, 69874, 107944, 84580, 84593.
Full patch (the entire server)

Given the volume (12528 lines in oc_previews at the time of diagnosis), complete regeneration in a dedicated tmux session:

tmux new -s preview_regen

CREATE TABLE oc_previews_backup_full_20260708 AS SELECT * FROM oc_previews;
DELETE FROM oc_previews;

sudo -u www-data php occ preview:generate-all -v 2>&1 | tee ~/preview_regen_20260708.log

Uninterrupted detachment : Ctrl+B then D. Resumption : tmux attachment -t preview_regen.

Progress monitoring during execution :

tail -f ~/preview_regen_20260708.log
sudo -u www-data php occ preview:queue-stats # asynchronous queue (previewgenerator), distinct from the job foreground

Final verification recommended after the end of the job:

SELECT COUNT(*) FROM oc_previews; -- must go up close or above 12528

ls -la /var/www/nextcloud/data/appdata_oc36r1xakj9s/preview///--on a random fileid

Limits and monitoring

This cleaning corrects the current state but does not correct the root cause on the Nextcloud side (still unsolved in ticket #56485 at the date of diagnosis). New orphaned entries can reappear on added/modified files later.