Re: A question about journal creation

Since closing the prevalent system and restarting it is a cost you are
willing to pay, if you do that before executing the transaction group,
a new journal will be created,

On Thu, Jul 25, 2013 at 2:15 PM, Paul Bennett <[email protected]> wrote:
> We have a situation where we would like to run a group of transactions, and
> be able to undo them as a group. We could define inverses on the
> transactions and re-run, but this is complicated. In the context in which
> they run, there would only be a single user on the system (an
> administrator). The system would leave the single-user context with either
> the group executed as normal, or not executed at all. There would be no
> other transactions executing on the system while this group is executed and
> possibly undone.
>
> Given these constraints, we think there is a simple implementation: simply
> remove from the journal those transactions that need to be undone. We would
> do this by taking a snapshot before the transactions are executed, starting
> a new journal, and executing the transactions. Then, to undo, we simply
> remove that new journal file, and reload the last snapshot.
>
> So:
>
> 1) Does this sound like a plausible solution? Have we missed something that
> makes this unworkable?
>
> 2) The only thing missing from this to be done is the ability to control
> explicitly the transaction boundaries on which a journal is created i.e.
> there is no equivalent of takeSnapshot() for starting a new journal.
> Obviously this has to be synced with execution and journal sync, so we would
> propose to implement this by adding a boolean to the execute(Transaction t)
> method, which would ultimately add a flag to TransactionCapsule, indicating
> it should explicitly start a new journal before serialization - similar to
> the test in PersistentJournal#append using the isOutputJournalStillValid()
> method.
>
> Does this sound like a good/viable solution?
>
> Any comments/alternative ideas would be most welcome!
>
> Thanks in advance,
>
> -pb
>
>
>
>
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-- 
Valeu, Klaus.

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