Possible Scoreboard Refresh Memory Leak

[gozzarda]

Description of the problem

Apparent memory leak observed when Jury scoreboard left running.
Mayb be a factor that this contest has 300+ teams and is multiple weeks long.
Seen as high as 10.8 GB memory usage and a whole CPU core.

Your environment

• DOMjudge v8.3.1
• Pop!_OS 24.04
• Chromium 138.0.7204.157

Steps to reproduce

1. Set up a new contest

• In my case, there are several contests, all weeks long, all with the same hundreds of teams, in case this is relevant.

2. Log in as a Jury user and open the scoreboard
3. Leave the scoreboard open for a significant period of time (overnight, for me)

• I do not know if users submitting during this time is necessary to trigger the issue, but I don't think so.

4. Observe high CPU and memory usage.

Expected behaviour

Reasonable memory usage.

Actual behaviour

Unreasonable memory usage (10+ GB)

Any other information that you want to share?

I had a little time to do some very quick profiling, and there seems to be a periodic (when the scoreboard refreshes?) leak of a bunch of <tr>s from the scoreboard. As observed on a fresh page it was a few kB of detached elements directly but about 5 MB indirect (I think, I forget the exact numbers, sorry).
It would take about 2000 such leaks to account for 10+ GB, which is about 16-18 hours with a scoreboard refresh every 30 seconds.

[meisterT]

Thanks for reporting! I have a potential fix in #3157 - can you try it out in your setup, whether it helps?