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Re: backend overlays

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?"

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

I think a more interesting question is how to support underlying DB
replacement in proxycache and allow access to the configuration
directives of that underlying DB.

        database ldap
        overlay proxycache hdb
        proxycache hdb directory /var/db/proxydb

Then one could add an overlay:
        proxycache hdb overlay syncprov
        proxycache hdb syncprov-sessionlog 100 


>Obviously one way to do so would be to add config mechanisms to proxycache so that its private database can be explicitly configured. The other thought that occurred to me was to declare overlays in the backend-specific config directives. Then whenever a backend of that type is used, it has these other overlays already included. The problem of course is that if the overlay needs any suffix-dependent configuration, there's no way to automate that.
>
>e.g.
>backend bdb
>overlay syncprov
>syncprov-sessionlog 100
>
>database bdb
>suffix o=foo
>...
>
>database bdb
>suffix o=bar
>...
>
>So each of the two bdb databases would automatically get the syncprov overlay attached with a default sessionlog setting of 100.
>
>And to the original point,
>
>database ldap
>overlay proxycache
>proxycache bdb 1000 10 20
>...
>
>would allow the proxy's local storage to provide data to other consumers...
>
>>p.
>>
>> 
>>
>>>Every now and then I look at things like the proxycache overlay with its
>>>internal database, and wonder if there would ever be a need to put an
>>>overlay on that database. I suppose one way to handle that would be to
>>>add explicit proxycache directives for configuring such a feature.
>>>Another thought that came to mind was being able to declare overlays
>>>inside a "backend" section, such that these overlays would automatically
>>>be instantiated whenever a particular type of backend is used. Comments?
>>>
>>>--
>>> -- Howard Chu
>>> Chief Architect, Symas Corp.       Director, Highland Sun
>>> http://www.symas.com               http://highlandsun.com/hyc
>>> Symas: Premier OpenSource Development and Support
>>>
>>>
>>>   
>>
>>
>> 
>
>
>-- 
> -- Howard Chu
> Chief Architect, Symas Corp.       Director, Highland Sun
> http://www.symas.com               http://highlandsun.com/hyc
> Symas: Premier OpenSource Development and Support