Bug 503586

Summary: Find / search feature is slow with huge scrollback buffers and terms that appear a large number of times, with Konsole appearing frozen while searching
Product: [Applications] konsole Reporter: kndevl
Component: generalAssignee: Konsole Developer <konsole-devel>
Status: RESOLVED FIXED    
Severity: normal CC: christoph, holdenrf2021, john.kizer, maxim.yegorushkin, nicolas.fella, postix
Priority: NOR Keywords: efficiency-and-performance, regression
Version First Reported In: 25.04.0   
Target Milestone: ---   
Platform: Other   
OS: Linux   
See Also: https://bugs.kde.org/show_bug.cgi?id=506880
Latest Commit: https://invent.kde.org/utilities/konsole/-/commit/ed1bf0b947dd468f141687829ca7892c11d34116?merge_request_iid=1103 Version Fixed In:
Sentry Crash Report:

Description kndevl 2025-04-30 18:44:26 UTC 
I often work with large scrollback buffers in Konsole. Recently, Konsole has started highlighting the lines on the scrollbar for search hits. With large buffers, this is quite slow (in the order of a few minutes) on a modern notebook cpu. This also freezes the UI so I can't really do anything else with Konsole.

Ideally Konsole should allow disabling this feature. Konsole should also disable this feature when the scrollback buffer size is set above a certain limit.

I believe this is a regression because Konsole had handled search in large buffers just fine before.
Comment 1 John Kizer 2025-05-05 05:09:36 UTC 
Hi - to help make sure that folks are reproducing and looking into the same behavior that you're seeing, can you please provide Steps to Reproduce this issue as detailed in the report template? The Community Wiki provides a reference for what sorts of details are helpful here: https://community.kde.org/Get_Involved/Issue_Reporting#Steps_to_Reproduce

Thanks!
Comment 2 kndevl 2025-05-05 23:54:30 UTC 
It's fairly trivial to reproduce with a large scrollback buffer, so I had elided the steps. Anyway, here are the steps

1. Change the Konsole profile -> Scrolling -> Scrollback: Unlimited 
2. Run `yes "foo bar foo" | head -n 100000`
3. Press Ctrl + Shift + F to open the search panel
4. Type "foo"
5. Konsole freezes for a while

If it does not freeze on your machine, increase 100000 to a larger number. 

Expected: 

1. Konsole must be usable when search runs (scrolling, clicks)
2. Search must continue to highlight matching tokens in the visible text while the full search is running

Actual:

1. Konsole freezes until search is complete
2. This is a major regression in the new version and completely breaks my workflow. Depending on the scrollback buffer, search is now unpredictable and freezes the terminal. Previously, one could search in large buffers without any delay. 

Because this is a regression and breaks a key feature of a typical linux terminal application, I think it should be more important than NORMAL priority.
Comment 3 John Kizer 2025-05-06 17:34:32 UTC 
Thanks! I can reproduce that extremely large buffers, and terms that appear many times, cause noticeable slowness with those steps - not at the level of a few minutes, but long enough to make the application appear frozen.

For later reference, the line highlighting code was merged in https://invent.kde.org/utilities/konsole/-/merge_requests/1061
Comment 4 kndevl 2025-05-06 17:43:05 UTC 
I ran a profiler to see if there were any quick hotspots I could fix by throwing a different data structure at it, but the profile was dominated by QTextStream internal methods. While the feature is certainly useful, I think throwing it behind a config toggle would be a good workaround for now.
Comment 6 John Kizer 2025-06-19 05:38:01 UTC 
Looks like the commits mentioned below have been merged into git master for Konsole. Thanks!
Comment 7 Christoph Cullmann 2025-08-21 17:33:43 UTC 
*** Bug 506065 has been marked as a duplicate of this bug. ***
Comment 8 Christoph Cullmann 2025-08-21 17:37:56 UTC 
*** Bug 503135 has been marked as a duplicate of this bug. ***