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Re: backend overlays

Kurt D. Zeilenga wrote:

At 05:54 AM 2/20/2005, Howard Chu wrote:

Pierangelo Masarati wrote:

If this is completely off-topic, please disregard.

Let me try again... The proxycache overlay sits on top of (e.g.) back-ldap. It also creates an instance of back-bdb for its local storage. This instance of back-bdb is totally private to the proxycache overlay, it is completely invisible to the rest of slapd so you can't configure anything special on top of it. The first question in my mind was "would you ever need to put another overlay on top of this private back-bdb?"

Now I got it :)

Well, if its "totally private to the overlay" and intended
to be invisible, adding some layer in between might cause havoc.

Well, of course things should be done with care; however, I think Howard's point makes a lot of sense. Think of the chain overlay, which actually hides a back-ldap instance; one might need, for some reason, to stack a rwm overlay on top of referral chaining only. In principle, we could just leave to each overlay (or, in general, module) that uses private databases the possibility to allow extra layers; this would require to design a sort of backover.c for each overlay (or module) that requires it. A natural evolution would be to provide a mechanism, which is ... overlays.


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