[ZODB-Dev] Re: Mirrored ZODBs

[Roché Compaan]

On Fri, 2006-07-14 at 08:58 +0200, Joachim Schmitz wrote:
> Roché Compaan schrieb:
> > 
> > If you have common add/edit methods in your app used by all of your
> > classes, you could do application level replication between Zopes. We
> > have written a small replication module for on of our apps that copes
> > extremely well with disconnected Zopes, and replicates a very compact
> > serialisation of commands to each other (as opposed to whole objects).
> > And they replicate both ways. We been using it for about 4 years in
> > production now.
> > 
> > I could send you an example if you want to evaluate this route.
> > 
> could you post it to the list, cause that would be very interesting for 
> us too.

No problem, but remember this is app specific and still works with the
ZODB distributed with Zope 2.7.

In summary, it works like this:

There are 3 classes: ReplicationLog, ReplicationTarget and
ReplogTransaction.

You add a ReplicationLog to your Zope app and add ReplicationTarget
instances inside it. You log transactions to a ReplicationLog by calling
it's "log" method e.g:

self.ReplicationLog.log(object, 'manage_edit', {'x': 1, 'y': 2})

where the first arg is the object, second arg is the method and the last
arg is mapping of values that should change.

The ReplicationLog serialises arguments in '_serialise_args' and this
will be the app specific part. You will for instance notice that we have
a special serialisation for something we call a "reference".

A cron job calls replicate on your ReplicationLog instance.

-- 
Roché Compaan
Upfront Systems                 http://www.upfrontsystems.co.za
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