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From Daniel Manzke <daniel.man...@googlemail.com>
Subject Re: Will OffHeapMemoryBuffer get fragmented over time?
Date Sun, 16 Oct 2011 12:27:40 GMT
How about the Idea Hadoop is working. Make the Size of the Slices
configurable and asume that the Values fit into it. Or small ones get into
One slice, but this ones are marked as dropable :)

Bye,
Daniel

Am Sonntag, 16. Oktober 2011 schrieb Ashish <paliwalashish@gmail.com>:
> On Sun, Oct 16, 2011 at 2:50 PM, Raffaele P. Guidi
> <raffaele.p.guidi@gmail.com> wrote:
>> It will, definitely. I had two solutions ready in my mind (that rely on
>> having more than one buffer active):
>>
>>   1. *Simplest, and fastest* but with *some drawbacks*: when
>>   buffer.isTooDefragmented() then simply buffer.clear() - you loose
>>   everything, but - hey, it's a cache, not a db
>
> IMHO, we can't assume that since its a cache, we can clear any buffer
> it at our own will.
> Cache entries must always be evicted based on what is configured by
> user. Also we need a very efficient way of
> finding when a buffer is too fragmented.
>
> Take a use case, we put an entry a few hundred KB in size, and a lot
> of entries which are few KB in size.
> So how would the implementation work in these scenario's. I am just
> thinking loud, we may already have this working, and I may not be
> aware of it :)
>
>>   2. *Less simple, slower, less drawbacks*: when
>>   buffer.isTooDefragmented() mark the buffer as readOnly and then foreach
(ptr
>>   in buffer) copy ptr.content in emptyBuffer and update ptr accordingly
>>
>> where *isTooFragmented==number_of_empty_pointers over total_pointers >
>> desirable quota*
>>
>> The first one could be accomplished during a put() operation
(buffer.clear
>> is a logical operation that takes no time) while the second should be
taken
>> care of by the background thread. Those quick&dirty solutions could of
>> course be replaced with real defragmentation algorithms - may taken from
>> various malloc() implementations, that are the original inspiration
>> http://en.wikipedia.org/wiki/Malloc#Implementations
>
> Lets experiment with different strategies and see which works best. I
> am yet to take a deep dive into the Pointer implementation :)
>
>>
>> Beside that: I think this was filed in github issue tracker as an
>> enhancement together with some more - I think I should re-file them in
JIRA.
>
> Missed that, actually this came up when I was implementing the sample.
>
>>
>> Ciao,
>>    R
>>
>> On Sun, Oct 16, 2011 at 9:31 AM, Ashish <paliwalashish@gmail.com> wrote:
>>
>>> Folks,
>>>
>>> Will the offHeapMemoryBuffer get fragmented over time? Say after a
>>> couple thousand get/remove operations, will the off-heap have start
>>> having holes in the Buffer?
>>>
>>> --
>>> thanks
>>> ashish
>>>
>>
>
>
>
> --
> thanks
> ashish
>
> Blog: http://www.ashishpaliwal.com/blog
> My Photo Galleries: http://www.pbase.com/ashishpaliwal
>

-- 
Viele Grüße/Best Regards

Daniel Manzke

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