LarsThiessenSep 27, 2025
It's understandable that Unreal needs to touch a lot of files when starting the editor. But what if I told you that more than 5500 of those files are not needed for the editor to start at all and are just adding multiple seconds to the editor launch time?
Let's fix this!
#UE5 #gamedev
https://larstofus.com/2025/09/27/speeding-up-the-unreal-editor-launch-by-not-opening-5500-files/
Speeding up the Unreal Editor launch by … not opening 5500 files?

In my last article I wrote about some tooltip optimization to reduce the start time of the Unreal Editor by 2-5 seconds. Turns out people do really care about their editor start time. So much that …

Larst Of Us
Show threadArseny Kapoulkine

@LarsThiessen Nice! FWIW I believe FindFirstFile needs to open the *directory* that is being scanned - not each file. There’s no syscall per file. It’s not super clear from the article if UE misuses the APIs or if it scans 5500 folders (which could be way more files naturally).

And also while folder scanning is actually quite efficient in Windows, you can have file system filters installed that slow down the process substantially. Notably, pretty much any antivirus software will be a problem.

Sep 28, 2025 at 3:07pmWeb
Show threadLarsThiessenSep 28, 2025
@zeux Thanks for the info, I was also a bit confused by that part. I also would have expected for only the folders to be opened, but in my profiling this wasn't the case, the profiler reported 4957 calls to "OpenFile" and in the end 5500 files were listed, so I assume this call to happen for every file (with the delta being explained by the profiler resolution).
But it's very possible that this is still not the ideal way 👀