Re: Food Tasting, Memory and Rolling Back Transactions.

William,

Thanks.  I appreciate the response.   I have inserted a comment below.

R

On Jul 25, 2009, at 5:02 PM, William Pietri wrote:

> Hi, Rick.
>
> Ross Rick wrote:
>> As I understand it, food tasting keeps a complete duplicate model set
>> in memory and runs the transaction against the duplicate first to
>> ensure that it is safe.
>>
>> 1.   Is that correct?
>>
>
> That's my understanding.
>
>> 2.   If it is correct then is it correct to presume that I can
>> effectively double the amount of memory available to storage by
>> turning it off.
>>
>
> That is correct.
>> 3.   If I turn it off, what are the ramifications?    It seems
>> possible that rolling back a transaction would then be my
>> responibility.   Is that correct?
>>
>
> The risk is that a transaction blows up in the middle, leaving your
> model in an inconsistent state, one that might not be what you'd get
> from replaying the log. I think of that less as being responsible for
> rolling back, and more for being responsible that your transactions
> never, ever break. But perhaps it amounts to the same thing.

I am perfectly fine with testing everything I can before executing the  
transaction.  My issue would be with the things that are somewhat out  
of my control, like say, memory allocation.   I suppose in that  
situation I would have to force the user to quit anyway, and only be  
losing the last transaction, but I'm not so sure that's gonna work.

In my case, a single delete can cause a number of cascading deletes,  
with additional reassignments, for example a delete of a tree node  
could cause leaves to be removed as well plus branches  to be moved to  
the parent of the deleted node

So I doubt my ability to accurately to correctly roll back.   In that  
case, as rare as one hopes they are, a transaction roll back is really  
just an app restart or damn near, if I turn off food tasting.    I'm  
not complaining, I am just trying to be sure that I understand.


>
>> Finally,  closing the Prevayler, this should release all memory,  
>> right?
>
> Subject to all the joys of the JVM, that's my understanding. I haven't
> verified that myself, though, as my Prevayler instances tend to be
> long-lived.
>
> William
>
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