Re: [ldapext] nfsv4 vs the ldap consistency model

[Howard Chu <hyc@highlandsun.com>]

Leif Johansson wrote:
> On Friday 21 November 2008 21:49:30 Howard Chu wrote:
> > Leif Johansson wrote:
> > > So I had a talk with the nfsv4 wg today (and on their list earlier). The
> > > are trying to build AFS-style volume location for NFS using LDAP and I
> > > think they may have a problem with the LDAP consistency model: i.e
> > > "eventually consistent" for a couple of their usecases.
> > >
> > > I won't go into details unless people particularly care but I think we
> > > may need an I-D (something for a bof in SF perhaps) describing a control
> > > which asks for the result of an update operation to be  delayed until a
> > > certain criterion (eg in the form of a compare condition) is fulfilled on
> > > all "slaves". Implementation details would differ depending on the
> > > precise way replication is done for that vendor.
> > >
> > > Does that sound like something you would
> > >
> > > a) barf at
> > > b) laugh at
> > > c) ignore
> > > d) review given that someone wrote it up?
> > Sounds like what's really wanted is a distributed transaction. Why not just
> > call it that?
>
> Not really - I don't think they need commit/rollback or the ability to modify
> multiple entries in a transaction.

Then my answer is (a) and (b).

You cannot guarantee that the update will succeed at all slaves, so 
abort/rollback is essential.

This is 2 phase commit, whether they think they want to handle multiple 
entries or not. In reality they are modifying multiple entries anyway, even if 
it's the "same" entry on each slave. This is a transaction, plain and simple.
--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/
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