It depends on how long the object lives. If it’s still being used after a
certain number of garbage collection cycles, it gets moved to tenured space,
and will never be garbage collected until the tenured space is full, i.e.
you’ve used everything you gave Java with -Xmx. OK, it’s not a real memory
leak, but it causes the java application to use more memory than it needs to.
There is a genuine memory leak in the code space that I’ve seen before; some
code does something I don’t understand to do with re-allocated classes, and
that does cause a genuine memory leak that can never be garbage collected at
all. I don’t remember the details though, and never understood it when I did
remember them.
Tim
On 25 Nov 2020, at 11:51, Jonathan Aquilina
<jaquil...@eagleeyet.net<mailto:jaquil...@eagleeyet.net>> wrote:
Tim correct me if I am wrong here.
Memory is allocated for as long as the object is being called or do you mean
the memory is always allocated regardless of the object being in scope and that
part of the programme being used or not?
Regards,
Jonathan
From: Beowulf <beowulf-boun...@beowulf.org<mailto:beowulf-boun...@beowulf.org>>
On Behalf Of Tim Cutts
Sent: 25 November 2020 12:40
To: Prentice Bisbal <pbis...@pppl.gov<mailto:pbis...@pppl.gov>>
Cc: Beowulf <beowulf@beowulf.org<mailto:beowulf@beowulf.org>>
Subject: Re: [Beowulf] [External] Re: Clustering vs Hadoop/spark [EXT]
Except of course, you do really. Java applications can end up with huge memory
leaks because the programmers really need to understand the mechanism when
objects get moved from Eden and Survivor space into Tenured space.
Tenured space never decreases, so every object which ends up there is allocated
memory for the life of the process. If that was actually an ephemeral object,
tough, you’ve lost the memory.
So ideally, the programmer needs to understand the size of their pile of
ephemeral objects and make sure the Eden/Survivor spaces are large enough,
otherwise they will have a memory leak. If they make the ephemeral spaces too
large, though, garbage collection takes more time and performance decreases, so
it’s a balance.
I’m not sure you can ever actually really get rid of the need to understand
memory allocation… you just push the problem around!
Tim
On 24 Nov 2020, at 18:32, Prentice Bisbal via Beowulf
<beowulf@beowulf.org<mailto:beowulf@beowulf.org>> wrote:
Also, with Java, you don't have to worry about low-level issues like freeing
and allocating memory and doing pointer arithmetic. Not having to worry about
those low-level issues allows a student to focus more on the programming
concepts. I knew I screw up dereferencing pointers A LOT when learning C and C++
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The Wellcome Sanger Institute is operated by Genome Research
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