Re: [Prevayler-discussion] Schema Evolution

[Klaus W. <kla...@ya...>]

An interesting twist to this would be to have "schema update transactions", more or less like
smalltalk does, amidst your regular transactions.

So you would have things like "AddAtributeTransaction", "RenameClassTransaction",
"ChangeAtributeType" which would work on the object schema (performing all necessary conversions
too) just like regular transaction work on the objects.

Perfectly testable, perfectly safe, perfectly manageable, perfectly impossible to do in Java.  :P

See you, Klaus.


--- S Doyle <sco...@ya...> wrote:
> All,
> 
> I wonder if the following idea would solve the schema evolution
> problem, albeit in a radical fashion...
> 
> Suppose that there were no snapshots and the only record of changes
> to the prevalent system was the transaction log.  The object model
> would be constructed by replaying transactions.
> 
> The object model could be changed at any time, and the transaction
> classes would have to be updated to work with the new object model.
> 
> The benefits may include:
> - no schema evolution problem
> - ThereCanOnlyBeOne would make more sense when applied to
> transactions as opposed to the object model
> - less possibility of not being able to recreate state when non-ECC
> ram is corrupted
> - this approach might work better with the HttPrevayler concept
> 
> The drawbacks may include:
> - references to other objects within a transaction would be trickier
> - no performance improvement by simply reloading a snapshot
>   - i.e. the full log would have to be replayed
> - maintenance of multiple versions of transaction may be necessary
> 
> Thoughts?
> Scot
> 
> 
> 	
> 		
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