[Nepomuk] [RFC] Nepomuk Resource naming convention

[Matthew Dawson]

On February 13, 2013 06:04:12 PM Vishesh Handa wrote:
> Hey everyone
> 
> As you know nepomuk follows the following naming scheme - nepomuk:/TYPE/UUID
> 
> - TYPE is either 'res' or 'ctx'.
> - UUID is a 36 characters long generated via QUuid
> 
> The UUID is supposed to be unique across one machine. It isn't meant to be
> globally unique. However, we cannot be positively sure that the uuid
> generated will be unique. So, we query nepomuk to make sure no other
> resource with the same uuid exists. This query is expensive!
> 
> It consumes about 10-13% of the execution time for certain tests
> (DataManagementModelBenchmarks::storeResources_email). I would like to move
> to a much simpler naming scheme - nepomuk:/TYPE/number. The number will be
> an increasing integer which will start from 0.
> 
> This way, we will not need to rely on uuid generation and won't have to
> query the database during each creation.
> 
> Comments?

As it has been explained to me, the chances of generating duplicate UUIDs is 
so small as to not exist (even taking into account such things as the Birthday 
Paradox).  I don't think worrying about it is worth it.

That being said, the increasing number thing is useful too.  Three issues I 
quickly forsee:
1) Is this a hot path?  Since only one id can generated at a time, it needs 
proper locking.
2) It is critically important that you store the integer before the new 
resource, since otherwise you may end up with a duplicate in case of system 
failures.  And checking for a duplicate's existance brings you back to square 
one.
3) What happens when the number wraps around (if that is possible)?

Matthew
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