Why does the Disk Cleanup tool's Windows Update Cleanup accept so long and consume and so much CPU?

Raymond

September 22nd, 2022

If you ask the Disk Cleanup tool to clean up Windows Update files, you lot may find that it takes a long time and consumes a lot of CPU. What the heck is it doing? How hard tin deleting files be?

The Windows Update Cleanup option is doing more than just deleting files. It's basically doing two things.

First, it does the equivalent of dism /Online /Cleanup-Image /StartComponentCleanup. This is a command that goes by the nickname deep make clean, and it scavenges the component catalog looking for components that are no longer beingness referenced. Usually, the organization automatically does component scavenging on a schedule maintenance task. The automatic scavenging has a policy of waiting 30 days earlier removing an unreferenced component, and information technology also has a self-imposed time limit of i hour. Merely the special command line to a higher place bypasses both the 30-day grace period and the 1-hour timeout. Unreferenced components are removed immediately, and the job will run to completion, even if it takes more an 60 minutes.

(I don't know if the one 60 minutes timeout is really meaningful in do. I suspect it's in that location but equally a backstop in example the scavenging procedure goes haywire.)

The other thing that the Windows Update Cleanup task does is check with the Wof­Should­Compress­Binaries function to run across whether the system would benefit from compression of system files. If so, so information technology takes the operating system files that aren't already compressed and compresses them, storing the outcome in the WofCompressedData alternate information stream, as I described some time agone.

The compression algorithm used past the Windows Overlay Filter is higher quality than a real-time pinch algorithm, and it'due south designed so that decompression is fast, merely compression is expensive. And that's the cost: Yous need to spend a lot of CPU fourth dimension to do the compression, which is why the Windows Update Cleanup is using so much CPU time.

And information technology's doing the expensive data pinch because it'south trying very difficult to free up disk space. Because that'southward presumably why you are running the Disk Cleanup tool.