[Zope] Zope Versions unusable?

[Jim Fulton]

Jochen Haeberle wrote:
> 
(snip)
> >Yes. It happens when you try to modify an an object
> >that has been modified in (another) version. When you
> >modify an object in a version, the object is locked and
> >can only be modified in that version.  The effect of a change
> >can be wideer than expected. For example, adding an object
> >to a folder modifies the folder.  If changing an
> >object causes a catalog to be updated, then changing
> >an object in a version locks the catalog, as well as
> >the object.
> 
> Mhm, not really. Only if you refer to the non Version environment as
> a a Version, too (what you probably do), well, then it is probably the
> catalog messing up...
> 
> But then, it is a real pain... how am I supposed to work on features in
> a version if I can't try it using the catalog...

This is currently an issue that limits the usefulness of
using versions and catalog together. It is a situation
that we plan to improve. :)

There are a number of things we can do to address this:

 1. Reduce the number of updates made when an object is
    added to the catalog.  For example, there is a problem
    with the current BTree implementation that causes too
    many nodes to get updated due to the way that tree-size
    information is stored in intermediate nodes. We are 
    working on fixing this.

 2. Add a ZODB conflict-resolution protocol.  This will allow
    application level code to resolve conflicts. For example, 
    imagine two requests that add items to a folder with 
    different names.  Currently, these requests conflict
    because they both modify the folder. In the future, 
    folders might implement methods that resolve the conflict
    by adding both items.
 
Jim

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