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Re: Cancellation and wc-ng txns

From: Hyrum K Wright <hyrum_at_hyrumwright.org>
Date: Fri, 22 Apr 2011 16:34:58 -0500

2011/4/22 Branko Čibej <brane_at_e-reka.si>:
> On 22.04.2011 23:11, Hyrum K Wright wrote:
>> What's the relationship between cancellation functions and
>> transactions in wc-ng?
>> In the interests of performance and correctness, we've been moving
>> toward a model where more and more gets done in a single wc-ng
>> transaction.  I've no problem with that, and like the atomicity and
>> speed it gives us, but how does that interact with our cancellation
>> functions?  Do we still check for cancellation from within the
>> transaction?  If the user cancels, do we rollback the transaction, or
>> commit it?
>> My question then is two-fold:
>>  * what actually happens today?
>>  * and what is the Right Thing to happen?
>> My own thoughts: we should check for cancellation, and if it occurs,
>> we should rollback the txn.
> If the transaction is so long-running that cancellation checks would
> make sense ... then something's wrong, as AFAIUI long-running
> transactions are frowned upon around here. Still, if that does happen,
> then the only thing you can do when an operation is canceled is to roll
> back the transaction -- anything else would be bound to produce invalid
> state in the database.

I would tend to agree on both points, and I also wonder if/how our
cancellation checks and handlers become a bit obsolete with atomic
database operations (which execute in only a few queries, rather than
a multitude of tree walks).

Received on 2011-04-22 23:35:27 CEST

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