[ZODB-Dev] Upgrading Zeo Server to 2.7

[Tim Peters]

[Martijn Jacobs]
> I know this might not be the right mailinglist, but I'm sure someone of
> you guys can answer my question :)
>
> We have a ZEO server running on zope 2.6.2 and zeo clients with zope
> versions 2.6.x Now we want to upgrade all our zope clients and servers to
> 2.7.4. The first step would be the ZEO server, and my question is :
>
> Can zope 2.6.x ZEO clients run with a 2.7 ZEO server? Are there any
> problems which might occure that are not to be seen in the first place?

It's before my time with ZODB, but scouring the old NEWS.txt files for ZODB
releases turns up this, from ZODB 3.2 alpha 1 (in January 2003):

    There is a new version of the ZEO protocol in this release and a
    first stab at protocol negotiation.  (It's a first stab because the
    protocol checking supporting in ZODB 3.1 was too primitive to support
    anything better.)  A ZODB 3.2 ZEO client can talk to an old server,
    but a ZODB 3.2 server can't talk to an old client.  It's safe to
    upgrade all the clients first and upgrade the server last.  The ZEO
    client cache format changed, so you'll need to delete persistent
    caches before restarting clients.

I've got no reason to suspect that more than that is true, although that
description doesn't really match my reading of the ZODB 3.2.5 protocol
negotiation code.

Don't really have time to play with it now, and never tried it myself.  I
hope someone who has tried it will share actual experience.  Else, as it
says, I'd stick to upgrading the clients first (and deleting their
persistent caches before restarting them).