4 ms·

Maybe they have to use some kind of legacy JVM library that doesn't work on Java 8? It looks like they're a GoLang shop, so I'm not sure why we'd assume their J

Maybe they have to use some kind of legacy JVM library that doesn't work on Java 8? It looks like they're a GoLang shop, so I'm not sure why we'd assume their Java stuff is representative of anything other than what they have to do because some useful JVM library for mapping or something needs to be supported.

erik_seaberg 5y ago
Yikes. Fortunately Java is a supported language at Uber, though some teams are more serious about it than others. Scala is also accepted because of Spark.
- viscanti 5y ago
  I guess I misunderstood things then. It's difficult to reconcile why they'd be using a legacy version of Java that required these specific GC tunings if they weren't forced to use it because of libraries that couldn't be replicated or replaced in GoLang. Sounds like it's a much bigger mess there than what I had assumed (I guess I was giving them too much of the benefit of the doubt).
_old_dude_ 5y ago
The problem is that Java 7 is 10 years old, it means that you are missing 10 years of optimization. For GCs that's a lot. GCs before ~2010 have been optimized for throughput more than for latency. Since then, you can choose. Since 10 years, G1 let you set your maximum pause time and you get a huge warning if it miss that target, ZGC or Shenandoah are from the beginning latency first, throughput second.
- lamontcg 5y ago
  I last tuned Java 6 in about ~2009 and I was a bit shocked at how familiar most of this article sounded... Like your handle, too.
- acamillo 5y ago
  Any advise on good / recent sources of information about the various GC algorithm in the recent JVM ?
vsto 5y ago
It is Hadoop that requires (mostly) Java 8 and Java 11 (runtime only). https://cwiki.apache.org/confluence/display/HADOOP/Hadoop+Java+Versions https://cwiki.apache.org/confluence/display/HADOOP/Hadoop+Ja...
- tomnipotent 5y ago
  That's for Hadoop 3 - Uber is on CDH 5 last I read, which has min support for Java 7 and it sounds like that's what they're using if the CMS GC was being used (unless it just happened to work better for them in Java 8+).

erik_seaberg 5y ago

Yikes. Fortunately Java is a supported language at Uber, though some teams are more serious about it than others. Scala is also accepted because of Spark.

viscanti 5y ago
I guess I misunderstood things then. It's difficult to reconcile why they'd be using a legacy version of Java that required these specific GC tunings if they weren't forced to use it because of libraries that couldn't be replicated or replaced in GoLang. Sounds like it's a much bigger mess there than what I had assumed (I guess I was giving them too much of the benefit of the doubt).

_old_dude_ 5y ago

The problem is that Java 7 is 10 years old, it means that you are missing 10 years of optimization. For GCs that's a lot. GCs before ~2010 have been optimized for throughput more than for latency. Since then, you can choose. Since 10 years, G1 let you set your maximum pause time and you get a huge warning if it miss that target, ZGC or Shenandoah are from the beginning latency first, throughput second.

lamontcg 5y ago
I last tuned Java 6 in about ~2009 and I was a bit shocked at how familiar most of this article sounded... Like your handle, too.
acamillo 5y ago
Any advise on good / recent sources of information about the various GC algorithm in the recent JVM ?

vsto 5y ago

It is Hadoop that requires (mostly) Java 8 and Java 11 (runtime only). https://cwiki.apache.org/confluence/display/HADOOP/Hadoop+Java+Versions https://cwiki.apache.org/confluence/display/HADOOP/Hadoop+Ja...

tomnipotent 5y ago
That's for Hadoop 3 - Uber is on CDH 5 last I read, which has min support for Java 7 and it sounds like that's what they're using if the CMS GC was being used (unless it just happened to work better for them in Java 8+).