Re: which GC optimizations work better with Clojure?

[Timothy Baldridge]

I should mention here that if you are tuning the GC anywhere except at the
end of your development cycle you're probably doing it wrong. 99% of the
time you'll get better performance by reviewing your algorithms, running a
CPU profiler, generating less garbage (via transients or something like
that),  or adding some missing type hints. You can spend a ton of time in
GC optimization, but I've never seen yield huge results. Maybe 10% here or
there, but I normally get orders of magnitude performance increases
spending just a few hours with a CPU profiler.

So it's one of those things where "if you don't know if you should change a
GC setting form the default, you probably don't".

On Sat, Apr 30, 2016 at 12:44 PM, Nando Breiter 
wrote:

> I've found Censum by jClarity to be an excellent tool to tune JVM GC
> parameters to your specific application running on a particular server. You
> add a few GC parameters to enable logging that the tool needs, run your app
> under load for enough time to get sufficient data, and then feed the log
> directly into Censum, which analyzes it and then suggests improvements that
> can be made to your GC parameters. There is also a list where you can ask
> questions about the analysis and its suggestions and get in depth replies
> from people who have extensive experience tuning JVMs.
>
> https://www.jclarity.com/censum/
>
>
>
> Aria Media Sagl
> +41 (0)76 303 4477 cell
> skype: ariamedia
>
> On Sat, Apr 30, 2016 at 11:50 AM, Niels van Klaveren <
> niels.vanklave...@gmail.com> wrote:
>
>> GC parameters used by a lot of projects are handed down like traditions
>> for years, even spreading to others. They're almost never re-evaluated,
>> which means they might actually lose out on new performance improvements,
>> or worse, might even cause performance regressions.
>>
>> Most parameters in the Overtone lib for instance have been the default
>> for quite some time (ParNew GC, TLAB). Where restricting New Gen might be a
>> good idea to reduce new gen GC latency, it can cause unwanted promotions,
>> longer tenured GC's and in the end heap fragmentation resulting in a full
>> defrag gc that can take 10s of seconds.
>>
>> Defaults are there for a reason, to take care of most situations. Any
>> settings other than the three default Garbage Collectors (Default for
>> shortest time to finish, CMS for shortest pause , G1 for short pauses but
>> long running times) and at most a pause hint for their heuristics means
>> you're entering case-specific  territory and should be treating it so.
>>
>> This means realistic benchmarking, profiling and comparisons between
>> different settings. I'd treat any JVM product or library with more than 2
>> GC parameters with care, because if they need so much tweaking as their
>> default, you can be sure to need both a good understanding of their inner
>> workings and JVM memory managent as well to keep them performing in your
>> specific case.
>>
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Re: which GC optimizations work better with Clojure?

[Nando Breiter]

I've found Censum by jClarity to be an excellent tool to tune JVM GC
parameters to your specific application running on a particular server. You
add a few GC parameters to enable logging that the tool needs, run your app
under load for enough time to get sufficient data, and then feed the log
directly into Censum, which analyzes it and then suggests improvements that
can be made to your GC parameters. There is also a list where you can ask
questions about the analysis and its suggestions and get in depth replies
from people who have extensive experience tuning JVMs.

https://www.jclarity.com/censum/



Aria Media Sagl
+41 (0)76 303 4477 cell
skype: ariamedia

On Sat, Apr 30, 2016 at 11:50 AM, Niels van Klaveren <
niels.vanklave...@gmail.com> wrote:

> GC parameters used by a lot of projects are handed down like traditions
> for years, even spreading to others. They're almost never re-evaluated,
> which means they might actually lose out on new performance improvements,
> or worse, might even cause performance regressions.
>
> Most parameters in the Overtone lib for instance have been the default for
> quite some time (ParNew GC, TLAB). Where restricting New Gen might be a
> good idea to reduce new gen GC latency, it can cause unwanted promotions,
> longer tenured GC's and in the end heap fragmentation resulting in a full
> defrag gc that can take 10s of seconds.
>
> Defaults are there for a reason, to take care of most situations. Any
> settings other than the three default Garbage Collectors (Default for
> shortest time to finish, CMS for shortest pause , G1 for short pauses but
> long running times) and at most a pause hint for their heuristics means
> you're entering case-specific  territory and should be treating it so.
>
> This means realistic benchmarking, profiling and comparisons between
> different settings. I'd treat any JVM product or library with more than 2
> GC parameters with care, because if they need so much tweaking as their
> default, you can be sure to need both a good understanding of their inner
> workings and JVM memory managent as well to keep them performing in your
> specific case.
>
> --
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which GC optimizations work better with Clojure?

[Niels van Klaveren]

GC parameters used by a lot of projects are handed down like traditions for 
years, even spreading to others. They're almost never re-evaluated, which means 
they might actually lose out on new performance improvements, or worse, might 
even cause performance regressions.

Most parameters in the Overtone lib for instance have been the default for 
quite some time (ParNew GC, TLAB). Where restricting New Gen might be a good 
idea to reduce new gen GC latency, it can cause unwanted promotions, longer 
tenured GC's and in the end heap fragmentation resulting in a full defrag gc 
that can take 10s of seconds.

Defaults are there for a reason, to take care of most situations. Any settings 
other than the three default Garbage Collectors (Default for shortest time to 
finish, CMS for shortest pause , G1 for short pauses but long running times) 
and at most a pause hint for their heuristics means you're entering 
case-specific  territory and should be treating it so.

This means realistic benchmarking, profiling and comparisons between different 
settings. I'd treat any JVM product or library with more than 2 GC parameters 
with care, because if they need so much tweaking as their default, you can be 
sure to need both a good understanding of their inner workings and JVM memory 
managent as well to keep them performing in your specific case.

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Re: which GC optimizations work better with Clojure?

[dennis zhuang]

It depends. CMS or G1 would be better in common cases as you said, clojure
runtime has many short-lived objects. We are using G1 in your production.
But sometimes you would prefer system throughput rather than GC pause time,
you may try Parallel GC.

2016-04-29 19:02 GMT+08:00 Camilo Roca :

>
> Following this thread:
> http://stackoverflow.com/questions/16695874/why-does-the-jvm-full-gc-need-to-stop-the-world
>
> I was wondering if anybody has some experience regarding GC optimizations
> that would work better for Clojure than the default: stop-the-world
> approach.
> My point being that given Clojure's immutable data structures, there is a
> lot of GC that is performed on young-objects which I guess could be
> optimized with some GC tweaks.
>
> Has anybody experience with something similar?
>
> So far the only reference that I have of a Clojure project using such
> optimizations is Overtone:
> https://github.com/overtone/overtone/blob/master/project.clj
>
> Which scenarios do you think that call for GC tweaks in Clojure?
>
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which GC optimizations work better with Clojure?

[Camilo Roca]

Following this thread: 
http://stackoverflow.com/questions/16695874/why-does-the-jvm-full-gc-need-to-stop-the-world

I was wondering if anybody has some experience regarding GC optimizations 
that would work better for Clojure than the default: stop-the-world 
approach.
My point being that given Clojure's immutable data structures, there is a 
lot of GC that is performed on young-objects which I guess could be 
optimized with some GC tweaks.

Has anybody experience with something similar?

So far the only reference that I have of a Clojure project using such 
optimizations is Overtone: 
https://github.com/overtone/overtone/blob/master/project.clj

Which scenarios do you think that call for GC tweaks in Clojure?

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