6 ms·

Tuning Java Servers (2014)

40 points by hemapani 11y ago

nailer 11y ago
Re: GC tuning, one investment bank simply disabled the GC during the trading day: purchasing massive amounts of RAM is cheap, having the GC non-deterministically kick in when you're making a decision or executing a trade is expensive. (Yes, Java isn't the most performant language but lots of developers know it and it's great for testing algos quickly)
- tootie 11y ago
  Isn't that just risking a crash? Why not just allocate a 300GB heap and hope GC kicks in rarely?
  - papercrane 11y ago
    Hoping the GC kicks in rarely is not a great strategy. Usually when I see something like this the developers have gone out of their way to write garbage-free code (see Coral Blocks for an example of this.)
    - rainhacker 11y ago
      If a code is truly garbage free (not sure how practical this is) won't it be independent of the heap size ? I know some teams do claim to write garbage free code to prevent GC from ever kicking of.
      - papercrane 11y ago
        Yeah, actually I think you're right. I don't think you can actually disable the GC in JVM unless you patch it. Truly garbage free is probably not practical 99% of the time. Normally you should just generally try to either have objects that are short-lived or practically permanent.
    - cam- 11y ago
      Agree, you want the GC sipping constantly, not gulping, or embarrassingly pulling up its pants.
- SourPatch 11y ago
  I assume that was a custom VM. As far as I know, there is no way to disable GC in the official Oracle JVM.
  - LoneWolf 11y ago
    I too would like to know that was the VM and how it was disabled.
  - nailer 11y ago
    I'm pretty sure it was a custom VM: I wasn't on the team, but my own group (Unix) was playing with custom IP stacks with the same goal (reducing latency, increasing determinism).
  - nradov 11y ago
    Can you do this with real-time Java? I understand that it allows you to do all your memory allocation first, then switch into real-time mode with no GC. http://www.oracle.com/technetwork/articles/java/nilsen-realtime-pt1-2264405.html http://www.oracle.com/technetwork/articles/java/nilsen-realt...
  - hemapani 11y ago
    With collectors like CMS, you can control after what percentage of the GC is filled GC will kick in. I think you can use that get the same effect. This is only for old gen.
- hemapani 11y ago
  You could get the same effect through off heap memory allocation.
- needusername 11y ago
  > disabled the GC Disabled the entire GC or just the old gen GC?

40 points by hemapani 11y ago

Re: GC tuning, one investment bank simply disabled the GC during the trading day: purchasing massive amounts of RAM is cheap, having the GC non-deterministically kick in when you're making a decision or executing a trade is expensive. (Yes, Java isn't the most performant language but lots of developers know it and it's great for testing algos quickly)

tootie 11y ago
Isn't that just risking a crash? Why not just allocate a 300GB heap and hope GC kicks in rarely?
- papercrane 11y ago
  Hoping the GC kicks in rarely is not a great strategy. Usually when I see something like this the developers have gone out of their way to write garbage-free code (see Coral Blocks for an example of this.)
  - rainhacker 11y ago
    If a code is truly garbage free (not sure how practical this is) won't it be independent of the heap size ? I know some teams do claim to write garbage free code to prevent GC from ever kicking of.
    - papercrane 11y ago
      Yeah, actually I think you're right. I don't think you can actually disable the GC in JVM unless you patch it. Truly garbage free is probably not practical 99% of the time. Normally you should just generally try to either have objects that are short-lived or practically permanent.
  - cam- 11y ago
    Agree, you want the GC sipping constantly, not gulping, or embarrassingly pulling up its pants.
SourPatch 11y ago
I assume that was a custom VM. As far as I know, there is no way to disable GC in the official Oracle JVM.
- LoneWolf 11y ago
  I too would like to know that was the VM and how it was disabled.
- nailer 11y ago
  I'm pretty sure it was a custom VM: I wasn't on the team, but my own group (Unix) was playing with custom IP stacks with the same goal (reducing latency, increasing determinism).
- nradov 11y ago
  Can you do this with real-time Java? I understand that it allows you to do all your memory allocation first, then switch into real-time mode with no GC. http://www.oracle.com/technetwork/articles/java/nilsen-realtime-pt1-2264405.html http://www.oracle.com/technetwork/articles/java/nilsen-realt...
- hemapani 11y ago
  With collectors like CMS, you can control after what percentage of the GC is filled GC will kick in. I think you can use that get the same effect. This is only for old gen.
hemapani 11y ago
You could get the same effect through off heap memory allocation.
needusername 11y ago
> disabled the GC Disabled the entire GC or just the old gen GC?