Webdav timeouts after updating to Snap 20.0.9snap2

[rlKoekie]

Describe the bug

After changing to 20.0.9snap2 (from 20.0.9snap1), connecting to the webdav fails or is very slow. I've searched the logs for errors, but none are thrown. The only suspicious thing I came across was a lot of these warnings in dmesg:
type=1400 audit(1621067221.119:882): apparmor="DENIED" operation="ptrace" profile="snap.nextcloud.nextcloud-cron" pid=23764 comm="ps" requested_mask="read" denied_mask="read" peer="unconfined"

I've reverted back to 20.0.9snap1 and my webdav started working fine again:
snap revert nextcloud
followed by nextcloud.occ files:scan --all to force an update of the file cache.

To Reproduce

mkdir /tmp/emptydir
sudo /bin/mount https://mynextcloud.address/remote.php/dav/files/myUserName/ /tmp/emptydir -t davfs -o user,uid=linuxusername,gid=linuxusername,dir_mode=750
This takes a very long time or hangs, issuing an "ls" on /tmp/emptydir then also hangs

Expected behavior

With 20.0.9snap1 the previous command instantly mounts, and giving an "ls" on the /tmp/emptydir folder returns contents quickly

OS/snapd/snap version

snap 2.50
snapd 2.50
series 16
ubuntu 18.04
kernel 5.4.0-74-generic

broken with: nextcloud 20.0.9snap2 27697 latest/stable nextcloud✓ -
works with: nextcloud 20.0.9snap1 27434 latest/stable nextcloud✓ -

Logs

Sorry, don't have those as I already reverted back and prefer not to break my nextcloud setup again. I can try to reproduce on a different machine if needed

[Fuseteam]

this is likely related to the mysql upgrade as noted here, it may take a while on a large database: #1626 (comment)

[rlKoekie]

I reverted back after 12-18 hours. All the other nextcloud functions (web view, desktop/Android client, passwords, etc) did work on the new snap. The only issue for me was slow webdav.
Is the database upgrade something that runs in the background after upgrading the snap? I did not see any significant cpu activity with slow webdav on the new snap.

[kyrofa]

Good thought @Fuseteam, but no @rlKoekie -- if you were able to access the web app then the upgrade completed successfully. My wife uses webdav as well and I'm all upgraded, so let me check with her and see if she's been having troubles.

[rlKoekie]

I've updated to snap 21.0.1snap1, and the webdav problem did not come back. All is well here, so I'm closing this issue. Thanks to everybody who looked into it!