[Seaside] transaction engines?

[Avi Bryant]

On Apr 28, 2004, at 4:44 PM, goran.krampe at bluefish.se wrote:

> radoslav hodnicak <rh at 4096.sk> wrote:
>> Does anybody happen to know/have an engine that implements 
>> transactions
>> for normal smalltalk objects? No external access or anything needed.
>
> Stephen Pair has made one called KATS:
> http://map1.squeakfoundation.org/sm/packagebyname/kats

The thing I don't like about KATS is that it's too ambitious: it tries 
to have the exact same instances of objects appear to have different 
state inside different transactions.  This means hacking the compiler 
so that inst var accesses are actually lookups in the current 
transaction, which is pretty intrusive.  In Seaside, I don't expect to 
share instances between sessions, and so having multiple copies of the 
same object (one per transaction) would be perfectly fine.  These could 
be brought in as-needed the same way an OODB does - when accessing an 
object for the first time in a new transaction, all of its references 
would be stubbed out, and local copies for those objects would be made 
the first time you tried to send them a message.  Even with nested 
transactions this would be pretty easy to manage, and a lot easier to 
debug.   Each transaction would keep a map from the original parent 
object to the local copy, for use when committing.   If you really 
needed an instance that lived longer than a single transaction, you 
could have a proxy that stored a root object and always forwarded its 
DNUs to the local equivalent in the current transaction - basically the 
same as the ReusableRef that Cees has mentioned using with OmniBase.

I've wanted to write a transaction engine like that for a while (I'm 
tired of writing half-assed equivalents that break on edge cases, eg, 
WAModelProxy), but haven't had time yet.  Rado, if you get started I'll 
pitch in.

Avi