All upgraders get registered at startup time

[Jan-Wijbrand Kolman]

On Zope startup time all Silva upgraders get registered at the upgrading
facility. Even though it might not use much, I think this is a waste of
resources (CPU and RAM). Esp. since most of the registrations are not useful
anyway - e.g the upgrader for 0.9.3 to 1.0 cannot be used if your running Silva-1.2.

Shouldn't the registration of the appropiate upgraders be done at upgrade-time?
Or at least, only the upgrader appropiate for a Silva version should be
regsitered at start up time? Or am I missing something here?

Currently assigned to me, but I'd like hear Zagy's and Faassen's idea on this.

[Christian Zagrodnick (zagy)]

Registring upgraders which you cannot use anyway should not be registered. This
indeed is a waste of ressources.

Registring at startup has a reason: third party products (i.e. SilvaDocument)
can register their upgraders. How could you do this at upgrade time? Start up is
the only 'easy' hook I know of. Although Silva has a list of Silva products,
which you could use on upgrade time. By the time implementing this using the
startup hook was the simplest thing to do.

[Jan-Wijbrand Kolman (jw-infrae)]

I removed the registration for upgraders to older versions of Silva. IOW only
the upgrader from the previous to *this* version is being regsitered.

Please test 1) if an upgrade from 1.1 to 1.2 still works correctly and, 2) other
functionality is not disrupted by this.

[Jan-Wijbrand Kolman (jw-infrae)]

Guido, could you please test this issue, (since you were quite actively involved
in the upgrade-machinerey recently)?