[Zope] More on understanding conflicts

[Chris McDonough]

>> Write conflicts happen for a transaction.  In Zope, there is one
>> transaction per request.
>
> There are two distinct sections to the navigation_box transaction.

There's a transaction for something named "navigation_box"?  Is this  
an IFRAME?

>   One
> where the session variables are read and a second where they are  
> used. To
> minimize conflicts, the what is now a single tranaction should be  
> split
> into two separate transactions.

Are you maybe misusing the term "transaction" here?  If this logic  
all happens in the course of a single request, it all happens in the  
same transaction unless that request causes, say, the reload of a frame.

There is a concept of a transaction here.  But it doesn't have  
anything to do with what happens during the course of a single  
request unless you explicitly try to control transactions, which is  
almost never a good idea.

> Any thought as to how to do that?  If navigation_box were broken into
> two separate methods, say nav_box1 and nav_box2, how does nav_box1
> commit itself and then transfer control and data (a session variable
> snapshot) to nav_box2 as a new transaction?

I suspect I don't understand what this would achieve.  Having more  
transactions will cause more conflicts.  Conflicts happen as a result  
of conflicting changes in two transactions.

> I would guess that if nav_box1 redirects to nav_box2 a new transaction
> is initiated and the old one committed.  Is that correct?  And is  
> there
> a better way to get the same effect?

I have no idea, sorry.

I think maybe what you might want to do here is to not use builtin  
Zope sessions. ;-)  Zope sessions rely on ZODB and are  
transactional.  If they didn't rely on ZODB, you wouldn't be getting  
conflict errors.  If they weren't transactional, you probably  
wouldn't notice.

Might be time to cut bait here.  We've been talking about this for  
months. ;-)  I think someone wrote a relational database backend for  
the sessioning API some time ago.  You may want to give that a shot.

- C