[ZODB-Dev] SQL/ZODB integration (was Re: ZODB and new styleclasses?)
Jim Fulton
jim@zope.com
Tue, 02 Jul 2002 14:38:08 -0400
Phillip J. Eby wrote:
...
>>last read are deactivated.
>>
>
> Right, and not all back-ends provide any kind of notification that lets you
> do this. I suppose you could reasonably consider this a deficiency of the
> back-ends rather than of the ZODB framework. :) But it's nonetheless a
> requirement for many people to use such back-ends. :)
This is a good point. I tend to take the invalidation protocol for granted.
I hope this doesn't prove fatal.
OTOH, I don't see how you can do an effective caching implimentation without
notification (invalidation). I wonder how other databases handle this.
Oracle does a lot of caching, I wonder if they have a notification model. I bet they
do. Does anyone know if Postgress caches on the client?
>
>
>>Note that we plan a major performance improvement that will cause
>>
> transactions to read
>
>>data committed as of the transaction start time even if newer data has
>>
> been committed.
>
>>This will assure consistency and serializability without producing as many
>>
> conflicts.
>
> Eeek! I can see this for CMS applications, but some applications really
> *need* pessimistic conflict detection, i.e. locking.
That's fair enough. That raises another possibly fatal issue.
I read a book once (Atomic Transactions, by William Weil) that gave a mathematical
proof that time-stamp protocols and locking protocols can be mixed in the same TM.
OTOH, I think few databases use locking protocols any more. Locking is certainly
hard to mix with object persistence. OTOH, I suspect you can get a pessimistic
time-stamp protocol.
> One thing that's illustrated very well by this little interchange is the
> need for a clear taxonomy and common working terminology in the new SIG,
> right from the start. :)
Yes.
Jim
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