RE: 9. "Replication of ACI changes"

["Albert Langer" <Albert.Langer@xxxxxxxxxxxxxxxxxxxxx>]

[Kurt]
At 10:53 PM 7/20/00 +1000, Albert Langer wrote:
>As you know I have not proposed an alternative to URP's basic approach for
>dealing with modifyDN, create and delete operations, but only for modify
>operations, since your approach to the former does maintain atomicity.

Does the fact that a modifyDN may change the entry's contents
have any impact upon this discussion?

[Albert]
Yes, thanks for mentioning that. Whenever modifyDN is not just a move to a
different superior with no change in the RDN, then it changes the contents
as well as the DN (unless it happens to just swap some distinguished and
non-distinguished attribute values and not add or remove any).

Thus there isn't a complete separation between the Directory Information
Base (DIB) aspects that MDCR deals with and the Directory Information Tree
(DIT) aspects that I have just assumed will be handled along the same lines
that URP proposes.

My assumption has really been that URP does handle the DIT aspects
atomically, imprecisely described by me above as also handling modifyDN
atomically, although as you point out, only create and delete are actually
always handled atomically. It is the URP's "basic approach" to DIT issues
that I agree with - eg renaming by adding the entryID as a distinguished
value when there are clashes.

I've just assumed that given both DIT and DIB aspects would be handled
atomically, there wouldn't be any major problem combining them into a single
atomic operation in which they either both eventually succeed or both
eventually fail (whether due to DIT integrity constraints, structure rules,
name forms, object class schema or any kind of access controls). This may in
fact require some of the "distinguished-not-present" complications in URP,
hopefully only when the operation has eventually failed by resulting in a
renaming anyway.

But I haven't attempted to think any of that through at all - just proposing
a method of dealing with DIB changes atomically and leaving DIT issues to be
worked out in detail later, hopefully together with the authors of URP, and
only when and if the WG decides to consider MDCR by adding it to its agenda
as a possible alternative. (I'd certainly rather leave thinking through that
stuff to people who have already thought a lot about it - ie Steve and
Alison).

That overlap may well further complicate handling ACI issues, but I simply
haven't thought about it yet. Do you have any specific thoughts on it?

For now, I think the simplest possible example of what happens when URP
merges independent changes to different attributes or attribute values will
do, without complicating the examples by considering modifyDN. Just changes
to (non-distinguished) ACI attributes for a single entry made at different
replicas will suffice to show this just HAS to be done atomically.