[Zope] Questions about demostorage

[Duncan Booth]

Can someone explain to me what is and is not safe to do with demostorage?

Say I have a zope setup involving a zeo server and clients, and I create 
another zope instance with <demostorage> wrapped around both <zeoclient> 
mounts (the catalogs are mounted separately from the rest of the content).
The main zope setup remains active while I'm using the demostorage setup, 
so content will be added/edited or deleted in the zeo zodb.

A bit of experimenting seems to indicate if I edit an object in the main 
system, the demostorage version picks up the changes until such time as I 
edit the same object in the demostorage instance. (So in other words, the 
connection from the demostorage front-end to the zeo-client isn't frozen at 
the point when the storage is opened which might have been a plausible 
alternative).

What I'm a little worried about is the catalog. I'd guess that there is no 
guarantee that the demostorage instance gets a catalog which is consistent 
with the rest of the data (so I could easily get site errors in the 
demostorage instance), but there should be no danger that any changes I 
make can affect the live site and restarting the demo instance would get it 
back into a consistent state, at least for a while. Is that a reasonable 
interpretation?

What I'm hoping to achieve is a way of testing upgrades on our live system 
in an environment as close as possible to the real live environment, but 
without actually affecting the live system in any way. Demostorage seems to 
offer that as an option.