[jira] [Issue Comment Edited] (DIRECTMEMORY-9) Add a defragmentation mechanism

["Michael André Pearce (Issue Comment Edited JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DIRECTMEMORY-9?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245630#comment-13245630 ] 

Michael André Pearce edited comment on DIRECTMEMORY-9 at 4/3/12 7:27 PM:
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Ok so have the old memory buffer (version 0.5) architecture working with merging memory and a defragmentation, also includes support for high concurrency, unfortunately i cannot seem to unpick the recent changes made in (version 0.6) that completely changed the memory buffer and its way of handling bits as it seems so wide spread in one hit, as such i supply the following solution if it can be introduced the old memory buffer or if the recent major changes that were done across the board were to be reverted I would be willing to supply a patch on the older. As this resolves not only the merging memory allocator it also resolves the other important issues i leave it to the group how to proceed.

this resolves in version 0.5 DIRECTMEMORY-40, DIRECTMEMORY-9 and also DIRECTMEMORY-74
                
      was (Author: teaandcoffee):
    Ok so have the old memory buffer architecture working with merging memory and a defragmentation, also includes support for high concurrency, unfortunately i cannot seem to unpick the recent changes that completely changed the memory buffer and its way of handling bits as it seems so wide spread in one hit, as such i supply the following solution if it can be introduced the old memory buffer or if the recent major changes that were done across the board were to be reverted I would be willing to supply a patch on the older. As this resolves not only the merging memory allocator it also resolves the other important issues i leave it to the group how to proceed.
                  
> 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
>              Labels: defrag,, defragmentation
>         Attachments: DIRECTMEMORY-9.zip, SANDBOX-IDEAS.zip
>
>
> 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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