On Wed, Nov 25, 2009 at 5:54 PM, philippe van dyck <[email protected]> wrote:
> Multiple side effects could be added in order to support merging, splitting
> or copying of one ES to another.
>
> I am in the process of writing the Infinispan ES (with an S3 store) and I
> would like to design a migration tool from one ES to another (infrastructure
> or version).
>
> I was thinking of some kind of "copy on write" side effect, with a background
> thread actually reading and writing all the entities in order to get rid of
> the previous ES once the copy is finished.
>
> WDYT ? Is there a better way to do this ?
I doubt that Copy-on-Write is feasible, since long lived read-only
entities would not 'migrate'.
In the past, I did the other way around, i.e.
ReadInNew
IfNotFound
MoveFromOldToNew
ReadInNew
This could potentially be cascaded across several generations.
Now, this can't be implemented using SideEffects, and instead a
Concern is required, which would do the "move+retry" invisibly to the
ES or UoW.
Cheers
--
Niclas Hedhman, Software Developer
http://www.qi4j.org - New Energy for Java
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