At 1:20 PM -0500 11/30/00, Erik D. Mueller-Harder wrote:
>At 9:22 -0800 11/30/00, Frank Schima wrote:
>
>>In Sybase 11, a Select inside a Transaction _will_ reflect all the changes
>>made before the Commit. If an outside user tries the query, they
>>will be locked out until the Transaction is complete. However it is
>>possible for an outside user to override that (I forget how
>>exactly) and read the current state of the locked records - which
>>will include all the uncommitted changes.
>>
>>Just to clarify: All changes actually occur and are stored in the
>>tables during a Transaction. A Rollback command will go back and
>>undo all changes based on the transaction log - whereas a Commit
>>will simply leave everything untouched and unlock the tables.
>>During a Transaction, everyone else is Locked out of the records
>>associated with the Transaction (actually Sybase 11 does page
>>locking not record locking - I'm not sure about Sybase 12).
>
>It's been a long time now, but I believe that this is exactly the
>same way that transaction processing in RMS (VMS's native file
>system) works.
RMS journaling is optional, but when it is enabled, yes, you can roll
back files to an earlier state if, for example, the system crashes
during a transaction (but that doesn't happen very often on VMS :-).
I think Frank's post makes clear how transactions generally work in
RDBMS's. It's not easy to do and I think there's a reason it's not
there in MySQL. I believe Microsoft introduced transactions in
Access 2.0 along with the Jet engine, but I seem to remember there
were a lot of problems with the initial implementation. Much as we
would all like to see this sooner rather than later in Valentina,
it's important that Ruslan take time to study up on it and evaluate
whether he even has the development time to devote to it.
--
____________________________________________
Craig A. Berry
mailto:craig.berry at psinetcs .D.OT com
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