I used to find the performance of LVP to be fine, but now it is unusable. It takes from 30s to several minutes to display a 145KB log entry, and uses 25-30% CPU during this time. This is with a single 500MB file open and no searches or highlights. Searching in the file also takes more than 30s.

I am using version 3.0.16.

Thanks for the update, but I think part of the problem is not related to large messages. I often find that opening dialogs takes many seconds. In the meantime it just displays a white box where the dialog should be:

When opening the find box, sometimes I am able to paste in some text and hit enter to close it before the dialog ever displays, but most of the time I just have to wait.

Given the amount of memory your machine has, I would guess there is a performance issue which is tying up the GUI thread.  One thing to try is switching to DirectX rendering.  

Aside from that, it would help if we could focus our performance testing.  Is there anything unusual you might be doing which is contributing to this issue?  Have you noticed any sudden degradation after using a particular feature?  You could also try turning features off in settings to see if that helps identify the problem area.

I don't think I am doing anything unusual other than using a custom PatternParser and setting the lookup strategy to Find all matches. I tend to have 1-10 512MB files open with several searches per file.

Thanks for the update.

Parsing does not occur on the main UI thread, so I don't think that is the issue.  5 GB of logs would significant.  How many searches are we talking about?  You should be able to determine this by looking at the highlight manager.    Also, do you notice any difference when you have fewer files open or fewer searches?

Opening the highlight manager took 1 minute and 10 seconds to display anything. After that it was nice and responsive. Currently I have 13 highlights and 20 searches open. I currently have 4-5 512MB files merged. I am not sure if it makes a difference how much I have open but I have the impression it is a bit faster but still very slow when there is only 1 small file open.