The Jellyfin project recently committed a large number of performance improvements to their master branch. I’ve tested these in the current unstable release and I’m pleased to report that they address the issue described in this topic.
The changes are slated to be released as part of Jellyfin 12.0, which will see an RC release soon, according to the project’s maintainer. (Likely waiting on the items in this list: Jellyfin 12.0 · GitHub)
Some bad news: The 12.0 release made generally available today does not seem to benefit from the performance improvement seen in the 12.0-RC series of releases (release candidate series). It’s actually worse than 10.11.11 from what I can tell. I’ve asked the Jellyfin maintainers for clarification.
That would be unexpected, but maybe there are some routines running in the background that are leading to some temporary slowness? The release notes seem to indicate these may take some time.
A full library scan is REQUIRED after upgrading. As part of fixing how alternate versions are stored, versions that Jellyfin grouped automatically, not ones you merged yourself, are cleared during the upgrade. Until you run the scan those versions will look like they are missing.
The first scan after upgrading will take significantly longer than normal, and some movies may appear as newly added. This is expected. Jellyfin now checks every item in your library against the files on disk to clear out leftovers from previous versions, and anything that was previously filed incorrectly gets corrected as it goes. Do not stop the server while migrations are running.
Upgraded today to 12.0. Library load times are definitely slower on Infuse than 10.11.11.