Jenkins takes up to 45 minutes to startup and shows up:
Please wait while Jenkins is getting ready to work
My setup has a thousand jobs, some of them having each a thousands more entries in their build history.
Using strace, I can confirm there is a few threads that are browsing the build history and opening build.xml files. Since we have a ton of them, that takes a very long time.
Attached is a JStack of the process. Thread 19970 was one of them confirmed to load build.xml in strace. The stack trace mentions jenkins.model.lazy.AbstractLazyLoadRunMap but then hudson.model.Run.reload() which in turns make it load all the build.xml files
I have noticed https://issues.jenkins-ci.org/browse/JENKINS-8754 that is about making Jenkins faster to start by using lazy loading of the jobs. That does not seems to lazy load them.
My downstream bug report is https://bugzilla.wikimedia.org/show_bug.cgi?id=47120