Hi Roan,

thanks for the reply!

> because recentchanges are are periodically purged, so cannot be used between
> arbitrary dates.
If you have control over wiki A, you can set $wgRCMaxAge to a higher
value. You could also do the updates more often so there's never more
than $wgRCMaxAge between them.
I think your best bet is to use list=recentchanges and update frequently.

Sure. However, for the cases I am thinking of, this isn't always under my control. E.g. I might not be able to convince wikipedia to keep much longer logs. (Or would keeping recent changes say for several months be feasible?)

> Question 2: Can you see a better way of doing this? Also, why won't
> generator=allpages work across namespaces? (I guess there my be a reason why
> that isn't possible to do easily.)
Because other parameters like apprefix don't work cross-namespace.
Requests to make list=allpages work cross-namespace have been made in
the past and denied because the benefits of the slight increase in
convenience (there are few namespaces anyway) don't outweigh the
complexity of preventing certain parameters from being used

I guess there isn't a simple way to make allow something like apnamespace=0|1|2|3 for the same reason? 
> action=query&prop=revisions&generator=allpages&rvstart=20090521000000
> but this doesn't work.
> So, my question 3: Do you know why this doesn't work?
This'll probably result in an error, since rvstart can't be used in
multi-page mode.

Sure, it generates an error. I guess it's not implemented for the same reason as the apnamespace issue, in that it would just add a lot of complexity.

I can see that there are certain things one doesn't want to allow generally because the complexity outweighs the benefits. On the other hand it seem strange though that I can't get easily get all 'events' between two dates. Would it somehow be possible to build an intermediate solution? E.g. would it be feasible to build a dedicated
that just solved that problem?

I guess in principle it's possible to build this, but it might be quite inefficient, seeing as maintenance/rebuildrecentchanges.php says "This takes several hours, depending on the database size and server configuration."