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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