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From "Raffaele P. Guidi (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DIRECTMEMORY-9) Add a defragmentation mechanism
Date Sun, 16 Oct 2011 09:40:11 GMT
Add a defragmentation mechanism
-------------------------------

                 Key: DIRECTMEMORY-9
                 URL: https://issues.apache.org/jira/browse/DIRECTMEMORY-9
             Project: Apache DirectMemory
          Issue Type: Task
            Reporter: Raffaele P. Guidi


Add a defragmentation mechanism 

>From the ML: (paliwalashish)
>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?
(Me:)
>It will, definitely. I had two solutions ready in my mind (that rely on having more than
one buffer active): 
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
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


See also https://github.com/raffaeleguidi/DirectMemory/issues/43

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