3 ms·

How would real-world JVM startup times matter in deployments?

by dividedbyzero 4y ago

imtringued 4y ago
You reboot and suddenly your CPU is at 100% for 20 minutes starting every web service...
- pgwhalen 4y ago
  If your CPU is at 100% for 20 minutes starting every web service, that is definitely your problem, not Java’s problem.
smolder 4y ago
JVM startup times make using it in Lambda or scaling container clusters awkward. Scaling can't happen fast enough for traffic spikes when the startup time and cold start performance is crap.
dboreham 4y ago
You exec a process expecting it to begin operating, providing some networked service, in a reasonable time. Instead it doesn't do that. It spends tens of seconds, sometimes minutes, running JIT and other sundry startup overhead. You may not have seen this if you haven't used Scala...
- thefaux 4y ago
  Yeah, Scala is absurdly bad for startup time because of poor modularization of the standard library. It's a decent language with a terrible standard library.
- dividedbyzero 4y ago
  Genuinely curious, what kind of application are you running? Which JVM are you using? Are you aggressively GC tuning? Very low on memory? I've used Scala from 2.8 up to 3.0, for microservice systems, monoliths, data pipelines, machine learning (way back), desktop apps for research using Swing, an Android app (worst idea ever), highly imperative to very functional, and I don't think I've ever seen anything remotely as bad as that even on genuinely big codebases. Hundreds of ms, sure, but minutes just getting the JVM up and running? I can see how that would be problematic.
  - dboreham 4y ago
    Ok, so to expand: applications that I've been responsible for from the beginning have not had long start up times. Where I've seen it is with other folks applications where I was hired as a consultant to look at performance. The most recent example was a Scala monolith. It had to use JVM 1.8 because <reasons> prevented migration to 11 (tried quite hard, but never succeeded). GC tuning doesn't really apply when considering start up delay, but yes it had been tuned over the years. Memory was not limited. The application, mainly due to Scala, had tens of thousands of classes. They all seemed to get JIT'ed on start up, which was the primary reason for the slow start up. People involved (who had come from heavy Scala shops like Twitter) seemed to think it was normal.

How would real-world JVM startup times matter in deployments?

imtringued 4y ago

You reboot and suddenly your CPU is at 100% for 20 minutes starting every web service...

pgwhalen 4y ago
If your CPU is at 100% for 20 minutes starting every web service, that is definitely your problem, not Java’s problem.

smolder 4y ago

JVM startup times make using it in Lambda or scaling container clusters awkward. Scaling can't happen fast enough for traffic spikes when the startup time and cold start performance is crap.

dboreham 4y ago

You exec a process expecting it to begin operating, providing some networked service, in a reasonable time. Instead it doesn't do that. It spends tens of seconds, sometimes minutes, running JIT and other sundry startup overhead. You may not have seen this if you haven't used Scala...

thefaux 4y ago
Yeah, Scala is absurdly bad for startup time because of poor modularization of the standard library. It's a decent language with a terrible standard library.
dividedbyzero 4y ago
Genuinely curious, what kind of application are you running? Which JVM are you using? Are you aggressively GC tuning? Very low on memory? I've used Scala from 2.8 up to 3.0, for microservice systems, monoliths, data pipelines, machine learning (way back), desktop apps for research using Swing, an Android app (worst idea ever), highly imperative to very functional, and I don't think I've ever seen anything remotely as bad as that even on genuinely big codebases. Hundreds of ms, sure, but minutes just getting the JVM up and running? I can see how that would be problematic.
- dboreham 4y ago
  Ok, so to expand: applications that I've been responsible for from the beginning have not had long start up times. Where I've seen it is with other folks applications where I was hired as a consultant to look at performance. The most recent example was a Scala monolith. It had to use JVM 1.8 because <reasons> prevented migration to 11 (tried quite hard, but never succeeded). GC tuning doesn't really apply when considering start up delay, but yes it had been tuned over the years. Memory was not limited. The application, mainly due to Scala, had tens of thousands of classes. They all seemed to get JIT'ed on start up, which was the primary reason for the slow start up. People involved (who had come from heavy Scala shops like Twitter) seemed to think it was normal.