Extremely slow page loading times

I run a basic Jenkins setup on my local network. No idea what’s changed to cause the problem but logging in and accessing any page takes ~1, sometimes up to 2 minutes! Page goes blank/white after 3 seconds then ages for the target page to display.

Jenkins is running on a 2018 6-core Intel Mac Mini, mostly we use Macs. I’ve tried shifting it onto an M4 Mini, but same problem so not a CPU speed problem; it was working fine on the same hardware up until recently.

Curiously, when accessing from a Windows 11 machine, instead of MacOs, pages load faster - some 20s, max 30s, which is very strange.

I had taken the controller & nodes with me when travelling to a different location but don’t think I’d changed any network-related Jenkins settings… although feels like probably some kind of network issue (running a 2.5GbE LAN without problems).

How on earth do I debug what’s causing the slowness?!

Any help much appreciated.

Jenkins: 2.541.3
OS: Mac OS X - 15.7.4
Java: 21.0.6 - Eclipse Adoptium (OpenJDK 64-Bit Server VM)
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Hi Justin,

The Mac vs Windows difference is a useful clue. The most likely cause is a DNS/IPv6 issue — macOS prefers IPv6 by default, and Jenkins can hang waiting for IPv6 resolution to time out before falling back to IPv4. Windows handles this fallback faster, which would explain the speed difference.

A few things worth trying:

  1. Add this JVM argument to your Jenkins startup configuration and restart Jenkins:
    -Djava.net.preferIPv4Stack=true

  2. Since you traveled to a different location recently, your DNS settings may have changed. Go to System Preferences → Network → Advanced → DNS and try switching to 8.8.8.8 (Google) or 1.1.1.1 (Cloudflare) temporarily to see if that makes a difference.

  3. You already have the Monitoring plugin installed. Go to Manage Jenkins → Monitoring and grab a thread dump during one of those slow page loads. It will show exactly where Jenkins is blocking, which will make diagnosis much more precise.

If none of the above helps, please share the thread dump output here — that will give a much clearer picture of what Jenkins is actually waiting on and help narrow it down further.

Hope this points you in the right direction!