Bug 511850

Summary: Rebuild Thumbnails results in digiKam hang "Not Responding"
Product: [Applications] digikam Reporter: CM <carlo.mj.m>
Component: Maintenance-ThumbsAssignee: Digikam Developers <digikam-bugs-null>
Status: RESOLVED FIXED    
Severity: normal CC: metzpinguin
Priority: NOR    
Version First Reported In: 8.8.0   
Target Milestone: ---   
Platform: Microsoft Windows   
OS: Microsoft Windows   
Latest Commit: https://invent.kde.org/graphics/digikam/-/commit/6ab4ffc1727fc835e7d9704b4da5766833d37623 Version Fixed/Implemented In: 9.0.0
Sentry Crash Report:

Description CM 2025-11-09 07:06:21 UTC 
First, is the "Rebuild Thumbnails" process going to allow me to scroll through images without having to wait for thumbnails to be generated? Sometimes, the thumbnails get generated too slowly by scrolling. Documentation (https://docs.digikam.org/en/maintenance_tools/maintenance_thumbnails.html) doesn't say that specifically.

When I try the "Rebuild Thumbnail" process, digiKam hangs (Task Manager shows high CPU usage by digiKam), and can't really tell if work is being done (UI is not responsive, "Not Responding"). Is progress supposed to be displayed in the status bar?

Library is 500,000+ photos. SQLite database.

digiKam: 8.8.0
KDE Frameworks: 6.17.0
Qt: Using 6.9.1 and built against 6.9.1
Windows 11 Version 25H2
Build ABI: x86_64-little_endian-llp64
Kernel: winnt 10.0.26200
Comment 1 Maik Qualmann 2025-11-09 08:27:27 UTC 
digiKam generates thumbnails "on the fly" while scrolling in the view. With new images, I don't notice any significant delay; sometimes you briefly see an empty icon that is then filled. When the thumbnails are later retrieved from the database, there's no delay at all.

What file types do you have in your albums?

Yes, if you generate thumbnails using the maintenance tool, there's a progress bar. However, there's a preliminary process that determines which items are affected. This could take a very long time for you with 500,000+ items and wouldn't show any progress. Here, with about 50,000 items in the database, this process takes about 2 seconds.

To be able to help here, we need DebugView logs.

Maik
Comment 2 Maik Qualmann 2025-11-09 09:27:36 UTC 
Git commit 6ab4ffc1727fc835e7d9704b4da5766833d37623 by Maik Qualmann.
Committed on 09/11/2025 at 09:26.
Pushed by mqualmann into branch 'master'.

calculate affected albums in a thread #1
FIXED-IN: 8.9.0

M  +1    -1    NEWS
M  +1    -0    core/utilities/maintenance/CMakeLists.txt
M  +54   -26   core/utilities/maintenance/tools/thumbs/thumbsgenerator.cpp
M  +2    -0    core/utilities/maintenance/tools/thumbs/thumbsgenerator.h

https://invent.kde.org/graphics/digikam/-/commit/6ab4ffc1727fc835e7d9704b4da5766833d37623
Comment 3 Maik Qualmann 2025-11-09 10:32:18 UTC 
Git commit 4f9b5531f9fd303147bf9ba1e19a9a9f498f8d15 by Maik Qualmann.
Committed on 09/11/2025 at 10:31.
Pushed by mqualmann into branch 'master'.

calculate affected albums in a thread #2

M  +55   -24   core/utilities/maintenance/tools/fingerprints/fingerprintsgenerator.cpp
M  +2    -0    core/utilities/maintenance/tools/fingerprints/fingerprintsgenerator.h

https://invent.kde.org/graphics/digikam/-/commit/4f9b5531f9fd303147bf9ba1e19a9a9f498f8d15
Comment 4 Maik Qualmann 2025-11-09 10:48:51 UTC 
Git commit d3c98f608cef447d26919effa7bd0eb6cbe5a4cc by Maik Qualmann.
Committed on 09/11/2025 at 10:48.
Pushed by mqualmann into branch 'master'.

calculate affected albums in a thread #3

M  +1    -1    core/utilities/maintenance/tools/fingerprints/fingerprintsgenerator.cpp
M  +48   -13   core/utilities/maintenance/tools/imgqsort/imagequalitysorter.cpp
M  +2    -0    core/utilities/maintenance/tools/imgqsort/imagequalitysorter.h

https://invent.kde.org/graphics/digikam/-/commit/d3c98f608cef447d26919effa7bd0eb6cbe5a4cc
Comment 5 CM 2025-11-09 18:18:52 UTC 
I have JPEGs.

I forgot to mention the thumbnails I mean are Face thumbnails for People tagging. Does Rebuild Thumbnails generate those, too?
Comment 6 Maik Qualmann 2025-11-09 18:23:56 UTC 
No, face thumbnails are not being created. We have already submitted a bug report about this.

Bug 466412

Maik
Comment 7 Maik Qualmann 2025-11-09 18:32:05 UTC 
Face thumbnails are actually created immediately during face detection scan in the current versions of digiKam and should be available along with the face. I'll check it again in the next few days.

Maik