So I decided to do a quick test using the Linux kernel source tree since it has lots of files. I duplicated a tree, used 'find . -type f -exec chmod 444 {} +' to make read only files for rsync to want to chmod, then used cp -al to make several duplicate trees using hard linked files. An rm -rf on one such tree took .97 seconds while an rsync deletion took 1.25 seconds. Clearly I need a bigger test to play with as that margin could easily change just by different outputs if either had a -v. But also, I did not experience the problem you are describing. My surviving hard links in the duplicate trees were still 444.

BTW, it seems that rsync uses unlink() while rm uses unlinkat(). No idea if/why there is a performance diff there but I didn't look into it as it is now time for me to go to work.

On 9/22/23 04:14, wrote:
On Thu, 2023-09-21 at 20:08 -0400, Kevin Korb via rsync wrote:

I have heard in the past that rsyncing an empty dir over a tree to
delete the tree is faster than an rm -rf but I can't say I have ever
benchmarked it to get any actual numbers.

This **may** indeed be a myth (for a long time now) re-cited again and again and
- could no longer be valid today
- could apply only when deleting explicitly named files but not deleting the 
complete folder
   (as we need to do in "Back in Time")

At least I could not find a holistic benchmark with many files and different 
(file systems, rsync'ing locally vs. over network, snapshot sizes, number of 
files, file sizes, rsync and rm versions...)

Q: Does `rsync` provide a test case that I could use as basis to prepare such a 
holistic benchmark?

But now that I am hearing
that rsync actually adds a bunch of pointless chmods to the process.  Is
it still faster given this problem?  If so maybe we should be trying to
investigate why rm is so slow.

Just by strace'ing I saw `rm` mainly calls unlink, `rsync` does not.

        Kevin Korb                      Phone:    (407) 252-6853
        Systems Administrator           Internet:
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