6 ms·

Wow! Amazing find. This is an amazingly well organized, detailed, useful resources. It might be worth adding (2013) or JDK7 to the title. Off the top of my hea

Wow! Amazing find. This is an amazingly well organized, detailed, useful resources. It might be worth adding (2013) or JDK7 to the title. Off the top of my head the details about the permgen don't apply anymore and I believe this predates G1.

pjmlp 8y ago
And in any case very specific to one JVM implementation, while there is a plethora of them around. https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#Active https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#... https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#Active_2 https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#...
- pvg 8y ago
  Most of it is generic enough to be applicable to anything that calls itself a JVM since it's required by spec. For instance, everything bytecodes, what a class file looks like, how dynamic linking works, etc.
  - pjmlp 8y ago
    Anyone that has had to track down issues between Sun(Oracle) and IBM caused by GC or JIT differences, will have a different opinion. I surely have been there a few times.
    - pvg 8y ago
      Why would you have a different opinion? This post is almost entirely not about stuff like that. If anything, the other linked thing in this thread 'JVM Anatomy' and this post should meet somewhere and agree to swap titles.
      - pjmlp 8y ago
        Because those things are left unspecified and they matter specially under heavy load. A JEE server might scale differently depending under which JVM it is running. The GC algorithm chosen by the implementation might lead to higher pauses in another JVM. The beautiful auto-vectorized code in one JVM might run like molasses in another JVM. One JVM might lack tiered compilation, thus increasing the saw shape pauses when it comes to JIT a specific method. Finally, the spec doesn't state how threads are executed, so they can be implemented as green or red threads, and certainly the code won't run the same way.
        pvg 8y ago
        Yeah I get that but the bulk of this article not about that at all. It's a sort of short, light appetizers and snacks overview of mostly spec-stuff.
        pjmlp 8y ago
        Faire enough, sorry for being pedantic.
        pvg 8y ago
        Hah, no, I'm in no position to be accepting apologies regarding pedantry.
- bitcharmer 8y ago
  It's true, but in practice Oracle's Hotspot is used in overwhelming majority of deployments you will get to work on.
  - pjmlp 8y ago
    Not when you work with corporations that love Websphere, embedded deployments or that little fork known as Android.
    - jxub 8y ago
      I recently attended a talk with Simon Ritter from Azul Systems that is developing Zing VM, and this VM is apparently gaining adoption among financial companies thanks to improved startup time and novel GC algorithms. Anyone with first hand production experience?
      - cmclaughlin 8y ago
        We use it at my job for our main api which needs lots of memory. I’m on the devops side and I don’t get into it much past the deployment of the app, so from my side it’s more of a hassle than openjdk since we have to deal with licensing.
      - yazr 8y ago
        Yes. Used in production HFT system. Works as advertised. But you should try the new J8 GC algos before you try a whole new VM
    - bitmapbrother 8y ago
      Android is not a fork of the JVM as it doesn't use the JVM. You seem to keep on parroting this fallacy.
      - pjmlp 8y ago
        Android started by copying Apache Harmony, as means of Google trying to avoid to pay Sun their rightful licenses, as confirmed by Andy Rubin emails. Thanks to that, Sun lost what might have rescued from insolvency. Which Google, while thinking that they finally got rid of Sun did not bothered to try to save. After the lawsuit and IBM's move to sponsor OpenJDK, Google was forced to migrate to OpenJDK. Yet Android does not use 100% of OpenJDK, rather they are adding little pieces of it in each Android version. Thus Android uses a forked version of OpenJDK, with everything that Google doesn't care removed from it. The fact that they use ART is an implementation detail, some Java certified JVMs for embeded deployment also have tooling to convert to their optimized implementation instead of using .class files. Rest assured, I am quite good parroting.
- hyperpape 8y ago
  I'm well aware that my knowledge of the JVM is almost exclusively about the Hotspot lineage, and a bit about Zing, which shares a lot of DNA, and I'd like to know more about the alternatives, but either I'm looking in the wrong places, or there's simply much less accessible information out there. My thought is that it would be better to spread information about the alternate implementations rather than exclusively complain about the misidentification.
  - pjmlp 8y ago
    Sorry for being pedantic, I just think mixing JVM with Hotspot is a bit like thinking GCC dictates what C is all about. Both are actually quite common misconceptions.
rzzzt 8y ago
Permgen evolved into the metaspace: https://dzone.com/articles/java-8-permgen-metaspace https://dzone.com/articles/java-8-permgen-metaspace
- jxub 8y ago
  And here's an Oracle blog post about it: https://blogs.oracle.com/poonam/entry/about_g1_garbage_collector_permanent https://blogs.oracle.com/poonam/entry/about_g1_garbage_colle...

pjmlp 8y ago

And in any case very specific to one JVM implementation, while there is a plethora of them around. https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#Active https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#... https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#Active_2 https://en.wikipedia.org/wiki/List_of_Java_virtual_machines#...

pvg 8y ago
Most of it is generic enough to be applicable to anything that calls itself a JVM since it's required by spec. For instance, everything bytecodes, what a class file looks like, how dynamic linking works, etc.
- pjmlp 8y ago
  Anyone that has had to track down issues between Sun(Oracle) and IBM caused by GC or JIT differences, will have a different opinion. I surely have been there a few times.
  - pvg 8y ago
    Why would you have a different opinion? This post is almost entirely not about stuff like that. If anything, the other linked thing in this thread 'JVM Anatomy' and this post should meet somewhere and agree to swap titles.
    - pjmlp 8y ago
      Because those things are left unspecified and they matter specially under heavy load. A JEE server might scale differently depending under which JVM it is running. The GC algorithm chosen by the implementation might lead to higher pauses in another JVM. The beautiful auto-vectorized code in one JVM might run like molasses in another JVM. One JVM might lack tiered compilation, thus increasing the saw shape pauses when it comes to JIT a specific method. Finally, the spec doesn't state how threads are executed, so they can be implemented as green or red threads, and certainly the code won't run the same way.
      - pvg 8y ago
        Yeah I get that but the bulk of this article not about that at all. It's a sort of short, light appetizers and snacks overview of mostly spec-stuff.
        pjmlp 8y ago
        Faire enough, sorry for being pedantic.
        pvg 8y ago
        Hah, no, I'm in no position to be accepting apologies regarding pedantry.
bitcharmer 8y ago
It's true, but in practice Oracle's Hotspot is used in overwhelming majority of deployments you will get to work on.
- pjmlp 8y ago
  Not when you work with corporations that love Websphere, embedded deployments or that little fork known as Android.
  - jxub 8y ago
    I recently attended a talk with Simon Ritter from Azul Systems that is developing Zing VM, and this VM is apparently gaining adoption among financial companies thanks to improved startup time and novel GC algorithms. Anyone with first hand production experience?
    - cmclaughlin 8y ago
      We use it at my job for our main api which needs lots of memory. I’m on the devops side and I don’t get into it much past the deployment of the app, so from my side it’s more of a hassle than openjdk since we have to deal with licensing.
    - yazr 8y ago
      Yes. Used in production HFT system. Works as advertised. But you should try the new J8 GC algos before you try a whole new VM
  - bitmapbrother 8y ago
    Android is not a fork of the JVM as it doesn't use the JVM. You seem to keep on parroting this fallacy.
    - pjmlp 8y ago
      Android started by copying Apache Harmony, as means of Google trying to avoid to pay Sun their rightful licenses, as confirmed by Andy Rubin emails. Thanks to that, Sun lost what might have rescued from insolvency. Which Google, while thinking that they finally got rid of Sun did not bothered to try to save. After the lawsuit and IBM's move to sponsor OpenJDK, Google was forced to migrate to OpenJDK. Yet Android does not use 100% of OpenJDK, rather they are adding little pieces of it in each Android version. Thus Android uses a forked version of OpenJDK, with everything that Google doesn't care removed from it. The fact that they use ART is an implementation detail, some Java certified JVMs for embeded deployment also have tooling to convert to their optimized implementation instead of using .class files. Rest assured, I am quite good parroting.
hyperpape 8y ago
I'm well aware that my knowledge of the JVM is almost exclusively about the Hotspot lineage, and a bit about Zing, which shares a lot of DNA, and I'd like to know more about the alternatives, but either I'm looking in the wrong places, or there's simply much less accessible information out there. My thought is that it would be better to spread information about the alternate implementations rather than exclusively complain about the misidentification.
- pjmlp 8y ago
  Sorry for being pedantic, I just think mixing JVM with Hotspot is a bit like thinking GCC dictates what C is all about. Both are actually quite common misconceptions.

rzzzt 8y ago

Permgen evolved into the metaspace: https://dzone.com/articles/java-8-permgen-metaspace https://dzone.com/articles/java-8-permgen-metaspace

jxub 8y ago
And here's an Oracle blog post about it: https://blogs.oracle.com/poonam/entry/about_g1_garbage_collector_permanent https://blogs.oracle.com/poonam/entry/about_g1_garbage_colle...