Re: Off-Heap Memory - simpler explanation than in docs

[Denis Magda]

You can give it a try and switch to OFFHEAP if it won’t work well for your use 
case.

However don’t forget to tune garbage collector appropriately. You can refer to 
this page [1] as an example.

[1] https://apacheignite.readme.io/docs/jvm-and-system-tuning 


—
Denis

> On May 21, 2016, at 6:09 PM, tomk  wrote:
> 
> So, 
> If each my node(machine)  has less  than 20 (in real 16) GB then I should
> use on-heap ?
> 
> 
> 
> --
> View this message in context: 
> http://apache-ignite-users.70518.x6.nabble.com/Off-Heap-Memory-simpler-explanation-than-in-docs-tp4790p5069.html
> Sent from the Apache Ignite Users mailing list archive at Nabble.com.

Re: Off-Heap Memory - simpler explanation than in docs

[tomk]

So, 
If each my node(machine)  has less  than 20 (in real 16) GB then I should
use on-heap ?



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Re: Off-Heap Memory - simpler explanation than in docs

[Denis Magda]

>  Why it is not possible with on heap ? 
Well-known garbage collectors that are available in Oracle/Open/IBM JDKs works 
not to nice with heaps of size > 20 GB on high-performant applications like the 
ones that are built on top of Ignite. The reason is that stop-the-world pauses 
can become lengthy measuring in tens or hundreds of seconds. Go though this 
discussion to get more details [1].

The only known garbage collector that can keep up with the heaps of hundreds of 
gygabates and that avoids stop-the-world pauses is Zing from Azul. [2]

Since you need to pay to Azul if you want to use its JVM the only possible way 
is to fall back to off-heap space in Ignite that will let to avoid lengthy GC 
pauses.

> Why off heap is faster than two others layers ?

It depends. Usually off-heap based solutions show comparable performance if 
properly tuned. However there can be minor performance degradation in high 
performant degradation since objects have to be moved from off-heap to on-heap 
when you need them (cache.get/results sets of SQL query/etc.). But as a benefit 
you won’t have long gc pauses.

[1] http://stackoverflow.com/questions/214362/java-very-large-heap-sizes 

[2] http://www.infoq.com/presentations/Understanding-Java-Garbage-Collection 


—
Denis

> On May 11, 2016, at 7:59 PM, tomk  wrote:
> 
> Thanks for your answer, nevertheless I still don't understand.  
> I know that nodes in ignite are launched in jvm.  
> It seems to me that off heap make it possible to cache large dataset (such
> large as RAM).  Why it is not possible with on heap ? 
> 
> Why off heap is faster than two others layers ?
> 
> 
> 
> --
> View this message in context: 
> http://apache-ignite-users.70518.x6.nabble.com/Off-Heap-Memory-simpler-explanation-than-in-docs-tp4790p4877.html
> Sent from the Apache Ignite Users mailing list archive at Nabble.com.

Re: Off-Heap Memory - simpler explanation than in docs

[tomk]

Thanks for your answer, nevertheless I still don't understand.  
I know that nodes in ignite are launched in jvm.  
It seems to me that off heap make it possible to cache large dataset (such
large as RAM).  Why it is not possible with on heap ? 

Why off heap is faster than two others layers ?



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Re: Off-Heap Memory - simpler explanation than in docs

[Pavel Tupitsyn]

Hi, what exactly is not clear?

When you create objects in Java, they end up on JVM heap, in managed
memory. These objects are subject to automatic garbage collection.
Ignite Off-Heap Memory feature stores cache data in unmanaged memory
(manual allocation/deallocation, like you do in C and other unmanaged
languages).
This reduces GC load (better performance, less GC pauses).

Let me know if this helps.

Pavel.

On Thu, May 5, 2016 at 5:08 PM, tomk  wrote:

> Hello,
> Could someone explain this in simpler way ? Maybe some intuition ?
>
>
>
> --
> View this message in context:
> http://apache-ignite-users.70518.x6.nabble.com/Off-Heap-Memory-simpler-explanation-than-in-docs-tp4790.html
> Sent from the Apache Ignite Users mailing list archive at Nabble.com.
>