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https://issues.apache.org/jira/browse/DIRECTMEMORY-63?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13211291#comment-13211291
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Raffaele P. Guidi commented on DIRECTMEMORY-63:
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Well, the general idea was, from the beginning, to keep "indexes" into the heap
and data outside the heap; I've made attempts at keeping the "index" part
(pointers and keys) as thin as possible and come up with Guava collections as
the better tradeoff. I also tried using CRC32 instead of keys but didn't work
out well (too hard to calculate). I meant to give Vanilla HugeCollections
(http://code.google.com/p/vanilla-java/wiki/HugeCollections - off-heap
collections of homogeneus objects) a try to make the Pointer's part even
lighter but still havent' had a chance to play with it (do someone knows the
thing?). Of course the most heavyweight part is now the key itself and maybe
it's worth a bit of hacking
> Investigate removing the need for an on heap map to store keys/pointers.
> ------------------------------------------------------------------------
>
> Key: DIRECTMEMORY-63
> URL: https://issues.apache.org/jira/browse/DIRECTMEMORY-63
> Project: Apache DirectMemory
> Issue Type: Improvement
> Reporter: Michael André Pearce
>
> On performance testing and monitoring jvm heap allocation, it became clear
> that as the off heap elements increased so did the on heap used memory. This
> is because DirectMemory is storing keys and pointers in the heap meaning that
> the cache isn't fully off heap, and on heap memory will increase linearly
> with elements in the cache.
> An idea maybe is to look into using a key's hash for location on a separate
> single off heap buffer to store the main heaps pointers.
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