I’ve noticed that, for a long time now, the MongoDB compilation for the many-collection-test has been taking around 4 hours (what?). This can be seen in all tasks executed in the waterfall over the past couple of months.

What’s most interesting is that the last message about how many files were processed is logged approximately 2–3 hours before the “Build completed” message. It’s a mystery what’s happening between these two messages that takes so much time.

[2025/11/18 13:21:55.306] Target //:install-mongod up-to-date:
[2025/11/18 13:21:55.708]   bazel-bin/install-mongod/bin/mongod
[2025/11/18 13:21:55.708] INFO: Elapsed time: 6713.693s, Critical Path: 377.33s
[2025/11/18 13:21:55.708] INFO: 8054 processes: 573 internal, 7378 linux-sandbox, 103 local.
[2025/11/18 16:21:56.426] INFO: Build completed successfully, 8054 total actions
[2025/11/18 16:21:56.426] Finished command 'shell.exec' in function 'compile mongodb' (step 6 of 13) in 4h53m23.66743142s.

I was able to identify that the first long execution happened here

However, the change there is very unlikely causing the problem, I suspect it is something else changed in the system.