[talk] Python

[Edward Capriolo]

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html
http://www.javaworld.com/article/2077408/core-java/sizeof-for-java.html
On Thursday, April 28, 2016, Edward Capriolo <edlinuxguru at gmail.com> wrote:

> The java class file format is well documented. Basically one pointer to
> the runtime class of the object followed by the object.
>
> If a given language is reference counted each object has one extra atomic
> field to count references.
>
> If a given language does not have objects but instead uses maps (that
> repeat the fields evey instance) that is going to be a more large object in
> memory.
>
> While i am not a large expert in this i believe javas approach is like a c
> struct with the exception the first word size bytes are a pointer to the
> type of class so that instances can be runtime inspected.
>
> Java also has a very clever system for compressing 64 bit pointers.. see
> compressedOOPs option. I have not heard much of this optimization anywhere
> else.
>
> On Thursday, April 28, 2016, Sujit K M <kmsujit at gmail.com
> <javascript:_e(%7B%7D,'cvml','kmsujit at gmail.com');>> wrote:
>
>> > Anecdotal. Keep in mind I have tested this and you can create 'a lot
>> more
>> > objects' given the same RAM than many other popular non java languages.
>> :)
>>
>> Could you please clarify further? I mean does it involve a object size
>> on the JVM.
>> How to measure the size occupied by the Object? How much extra space the
>> JVM
>> needs? What is JDK Feature that Let's you claim this?
>>
>> I have serious questions regarding this claim. As Interpreted or JIT
>> compiled languages
>> should in reality occupy more space.
>>
>> >
>> > On Wed, Apr 27, 2016 at 4:13 PM, Pete Wright <pete at nomadlogic.org>
>> wrote:
>> >>
>> >>
>> >>
>> >> On 04/26/2016 03:56 AM, Brian Coca wrote:
>> >>>
>> >>> As many a Java dev has told me: "the only problem is that you did not
>> >>> install enough RAM, just add it, it's cheap!"
>> >>>
>> >>>
>> >>
>> >> and therein is the issue - in practice i've found that by adding more
>> >> memory to a JVM heap will tend to worsen GC pauses, especially for
>> latency
>> >> sensitive operations.  then you get to do all sorts of fun stuff like
>> >> storing cached objects outside of the JVM or lord knows what.
>> >>
>> >> i spent about 3 months trying to help a team tune their java app when
>> they
>> >> noticed it would periodically show latencies of several seconds. they
>> kept
>> >> adding more memory to the heap, which made things worse.  once we
>> turned on
>> >> debugging metrics for GC it became painfully apparent that due to the
>> huge
>> >> heap that they had allocated GC was taking ages to complete and
>> stopping to
>> >> world in the process.  good times :)
>> >>
>> >> -pete
>> >>
>> >> --
>> >> Pete Wright
>> >> pete at nomadlogic.org
>> >>
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>> >
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>
>
> --
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> usual.
>


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