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From Emmanuel Lecharny <>
Subject Re: Replication configuration : second thought
Date Mon, 16 Mar 2009 16:10:37 GMT

> Regarding Repl Terminology
> ----------------------------------------
> OK let's get religious about using replication specific terminology.
> Instead of talking about client, server, master, slave, let's use the terms
> supplier and consumer.  The reason why I like these terms besides their
> common use is because it clearly denotes directionality and breaks down
> elements of the replication agreements to their atomic components. So I'd
> like to think in terms of a consumer configuration (with replication
> agreement) and a supplier configuration (also with a repl-agmt).
Totally +1. This is why I added them in (). So let's use them exclusively.
> Regarding Configuration
> -----------------------------------
> On a separate note, I've been torn between two ways of thinking about
> configuration for some time.  Regardless of whether we're talking about
> replication subsystem or not, we could apply this general discussion to any
> feature/facet of the server which also contains an interceptor.  So this
> discussion applies across the board as a configuration issue.
> So where do we configure a subsystem? In the interceptor configuration? Or
> as a separate component under the directory service.  Over the years I've
> made many mistakes with this stuff.  I like the idea of having a high level
> subsystem bean that contains all the configuration for the feature in one
> place instead of being distributed all over the configuration tree.
> Localization is always good because then the user and developer only needs
> to goto one place to get this information or modify the code for it.  It's
> more manageable.
That could lead to a centralized configuration in the DiT...
> I was always uncomfortable with bloating these interceptors with code.
> Instead I just wanted to leave them as simple hooks that funneled events
> (calls) into the subsystem.  The intercetor is then a simple listener that
> belongs to the subsystem in question. So the listener detects events and
> shuffles them into the subsystem to properly respond.  This allows us to
> keep the configuration in the top level subsystem facade while properly
> designing the various parts of the subsystem underneath with clarity instead
> of jamming all the subsystem handling logic tightly into interceptors which
> leads to code bloat in the interceptor modules leading to a jumbled up mess
> that is hard to manage.
In fact, there are _very few_ interceptors that need a configuration :
 - Authentication (takes a list of authenticators, something we may want 
to be global too)
 - Journal ( but this is a new interceptor, and the configuration is not 
yet stabilized)
 - Replication, but this is exactly what we are discussing about
and that's it.

So far, there is nothing that prevent us to get rid of any parameter in 
all the interceptors...
> So I recommend the following:
>   (1) Implement a subsystem for replication with a top level facade bean
> that can be configured via XBean.
>   (2) Setup a means to setup a set of replication agreements.  The same DSA
> can be both a consumer and a supplier to many other DSAs.  So we'll have a
> set of consumer agreements and a set of supplier agreements.
>   (3) Build the interceptor out to be just a simple hook into other Classes
> in the subsystem.  Make the subsystem return values for LDAP methods in the
> chain that require return values.
>   (4) Don't wory about adding the replication intercetor to the chain via
> XBean, just have the subsystem inject the intercetor programatically.  The
> user does not need to know this interceptor even exists right?
this can be discussed further, as this question is a bit too wide right 
now. Let's use the mechanism we have right now.
> DirectoryService vs. LdapServer
> ----------------------------------------------
> Now I don't know the answer to this but something itches me about putting
> the replication subsystem into the DirectoryService.  For some time now the
> DS corresponding to the top level facade representing what we always refered
> to as the core.  The core was never supposed to be networked because then
> that would pull dependencies like MINA.  It was the frontend that had
> network capability.  I know mitosis broke from this but seems the moron who
> wrote it broke all the rules.
what about having an embedded server with replication capability ?
> Question is do we want replication to be a high level system in the frontend
> since it leverages the protocol? Or do we want it in the DS which was
> traditionally core services without networking?
that's a good question... I would tend to think that injecting the 
replication subsystem into the core server is probably a better way, as 
it will be available not only to the standalone server, but also for an 
embedded server (all in all, the networked server just embedded the core...)

cordialement, regards,
Emmanuel Lécharny

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