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From Emmanuel Lecharny <elecha...@apache.org>
Subject Re: [DRS] thoughts about implementation
Date Wed, 04 Feb 2009 07:54:36 GMT
Alex Karasulu wrote:
> Hmm I see what you're thinking.  I think we're all having problems drawing
> distinctions between these various facilities in the server.  I know I have
> wavered myself.
>
> At first I was thinking we should have an extremely simple journal with
> markers tracking application of operations. Some conversations with Emmanuel
> then lead me to believe that using the CL as the journal was just as good.
> Now I feel it might not be such a good idea.  Let me list my thoughts:
>
> (1) The CL is highly indexed with several db files which means there will be
> many writes need to persist the record while keeping the CL and it's indices
> consistent.  Also the CL is deep inside the server in the interceptor chain
> and many things can go wrong while getting to that point, not to mention the
> processing time it takes to get there.
>
> (2) The CL should be used for auditing, versioning, snapshoting, and
> replication.  It is fast thanks to indices and will should all the
> operations that have succeeded in inducing changes.  It would get more
> complicated if we started using it to also capture operations before they
> have been applied.  The semantics would shift.
>
> (3) As you say the CL itself can get corrupted.  And for this reason it's
> not well suited as a journal for all (even in progress) operations.
>
> I'm seriously thinking the use of the CL for a journal is not a good
> decision. The journal needs to be fast and simple, doing only one thing and
> doing it fast and flawlessly.
>   
Seems like we are now converging on the same vision :) The journal must 
be as fast as possible, and dedicated to a very basic usage : DRS

For replication, we need a slightly more complex data structure, thus 
the CL.

But we can just see the CL as a bunch of indexes built on top of the 
journal.

-- 
--
cordialement, regards,
Emmanuel L├ęcharny
www.iktek.com
directory.apache.org



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