[Zope] Questions about demostorage

[Chris Withers]

Duncan Booth wrote:
> Can someone explain to me what is and is not safe to do with demostorage?

Well, that's a bit of a broad question ;-)

> Say I have a zope setup involving a zeo server and clients, and I create 
> another zope instance with <demostorage> wrapped around both <zeoclient> 

Why would you do that?!

> 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. 

Yep.

> (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).

Urm, that would involve taking a complete copy of the db at open time...

> 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?

...ish. But really, what you're doing is not what DemoStorage was 
designed for and will likely end in tears or a lot of hair pulling...

> 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.

It really doesn't ;-) Do this kinda testing the same way that everyone 
does: build yourself a uat environment that mirrors your production 
environment, maybe with a few less zeo clients, run it off a copy of 
your production zodb and then test there...

cheers,

Chris

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