[Zope-DB] RFC: mxODBCZopeDA & ZEO

Charlie Clark charlie at egenix.com
Wed May 26 13:39:57 EDT 2004

On 2004-05-25 at 18:38:19 [+0200], Chris Withers <chris at simplistix.co.uk> 
> Network shares, Subversion, etc...
> Myself? I setup a whole instance in Subversion and check it out onto any 
> machien
> I want a client one...

Interesting. I assume this involves using some kind of file storage?

> >>>3) heterogeneous clients may in some circumstances confuse each other
> >>>configuration
> >>
> >>How?
> > 
> > take the mxODBCZopeDA for example: if a connection is configured to talk 
> > to
> > DSN=Chris or use a specific driver then this may not on all clients.
> Ooo... ouch, yeah. Sounds like a system architecture problem. This is part 
> of
> cluster "being hard". Generally, having homogeneous nodes in a cluster is 
> the
> way to go, in which case the situation you describe shouldn't apply...

Yes, wasn't possible in the test configuration but maybe useful for support 
enquiries. Non-heterogeneous clients are likely to cause problems in 
load-balancing anyway.
> > This is an RFC targetted at those with real-life ZEO installations with
> > RDBMS. The example you cite is one where I think it might make more sense 
> > to
> > have a single connection
> explain what you mean by connection.

>From website to cluster. The current state sets up identical copies of the 
connection object in the various ZEO clients. They have to communicate 
through a local ODBC manager with the database. In a sense this goes against 
something like the mxODBCZopeDA which should be able to handle all necessary 
connections from all ZEO clients in a single object. This looks like it's 
going to remain a theoretical difference as there is unlikely to be any 
performance difference either way.

We're essentially looking at the question: what does ZEO give you and how 
does it work?

However, it looks like the common setup avoids the pitfalls of separate 
physical installations.
> > talking to several clients which do the rendering.
> explain what you mean by client.

> > But we don't really know how much ZEO is out there and how much of it uses
> > Zope-DAs. We know that the mxODBCZopeDA works with ZEO but maybe it could
> > work better.
> explain what you mean by "works with zeo"
> And there's PLENTY of ZEO out there ;-)

That's good to hear. There doesn't seem to be much running with the 
mxODBCZopeDA which seems to suggest that such sites primarily use the ZODB 
for storage.


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