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From Julien Vermillard <>
Subject Re: MapDB
Date Sat, 10 Nov 2012 15:36:13 GMT
Hi, just a small comment.
As mapDB use memory mapped files (mmap) using it for offloading memory to
disk is probably not a performing idea since the O/S will already cache the
file in memory the file for you :

You will basicly have two memoery cache and the O/S will beat the
directmemory one.

My 2 cents,


On Wed, Nov 7, 2012 at 8:54 AM, Raffaele P. Guidi <> wrote:

> Hi and thanks for your interest and offer! I know and appreciate your
> project and made plans to integrate it as disk store since the early days.
> We sure need good serialization libraries, in fact, in addition to provide
> support for many different ones (kryo, msgpack, protostuff, etc) we
> recently welcomed lightning (an unsafe based serializer by Christophe
> Engelbert) as a subproject to complement our codebase with a fast (and
> in-house) choice.
> I think we have more than one reason to integrate and share code:
>    1. DirectMemory could make good use of mapdb to serialize least
>    frequently used items to disk and free memory
>    2. DirectMemory could implement a MapDB disk based store in addition to
>    the bytebuffer and unsafe ones
>    3. MapDB could take advantage of DM's componentization approach to
>    support multiple serializers (we believe each one has its advantages in
>    different scenarios)
>    4. MapDB could use DM to write items to an off-heap before writing to
>    disk (asynchronously) to improve speed
>    5. We could merge our serialization efforts (I believe lightning is very
>    fast and worth to be considered) and provide an even better solution or
> two
>    alternative implementations
> In both cases we would be open to contribution in different forms - just
> contributing patches or with you to join us and the ASF as module or
> subproject (the latter options have to undergo a formal vote by all project
> members, of course) as I strongly believe that merging efforts would bring
> to a better and more complete product.
> What do you think about it?
> Regards,
>     Raffaele

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