Re: Deterministic UUID?

Hi Karl,

My first thought was, naturally, passing the host identifier in as part of
each transaction.

You could also store the host identifier somewhere inside your prevalent
system, and execute a transaction to set it when the app starts up.

If you know which transactions will need UUIDs (and how many), you could
create the UUIDs themselves at transaction-creation time. This is probably
closest to what I'd do most often.

Another idea might be to have a pool of precreated but unassigned UUIDs
inside the prevalent system, and have a transaction that adds a batch of new
UUIDs to the pool. The UUIDs would be created by whatever nondeterministic
means you like, outside of the prevalent system. Whenever you need a new
UUID inside some other transaction, just remove the next one from the pool.

Yet another idea, rather more hardcore, would be to store a strong
pseudorandom number generator in your prevalent system, seed it with
high-entropy random data with a transaction at app startup, and produce
random UUIDs (which don't need host identifiers) rather than time-based
UUIDs.

Cheers,
Justin


On Mon, Jan 11, 2010 at 12:43 AM, Karl Wettin <[email protected]> wrote:

> Due to several reasons I like my UUIDs, but as they are non
> deterministic they cause a problem for Prevayler.
>
> So based on execution time and a sequence number I implemented this 10
> byte identity I call DUID, deterministic unique identifier. To get all
> the features of an UUID in there (except for the universal part) it
> would be nice to add the final 6 bytes of host identification in there
> too. I suppose that would mean an application and cluster node
> identitity. Is there something existing in the Prevayler API that I
> can use for this? The only deterministic solution I can think of is to
> implement a transaction superclass that contains these values,
> automatically initialized via some config file/spring/what not.
>
>
>     karl
>
>

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