[ZODB-Dev] What's the deal with _p_independent?

[Jim Fulton]

On Jul 7, 2007, at 6:42 AM, Stefan H. Holek wrote:

> BTrees.Length is used in many places to maintain the length of  
> BTrees. Just the other day it was added to  
> zope.app.container.btree. While I am happy about the speed  
> improvements, I am concerned about the fact that BTrees.Length  
> declares itself _p_independent. I'd like some clarification about  
> what happens in a conflict resolution situation, when the Length is  
> _p_independent but the BTree itself is not. I *think* that with  
> MVCC this means a read-conflict will reset the BTree, but not it's  
> Length.
>
> All I could google up is this from 2004: http://mail.zope.org/ 
> pipermail/zodb-dev/2004-April/007269.html
>
> Now, do we need another Length class or is BTrees.Length just fine  
> and dandy?

Thanks for bringing this up.  Looking at this again, I fail to see  
the point of _p_independent in the presence of MVCC.  The API was  
originally added to avoid read conflicts when we read dirty data.   
With MVCC we no-longer read dirty data.  Unless I'm missing  
something, I'd like to just drop the concept altogether.

Would you mind creating a launchpad issue to that effect?

Jim

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