Wikimedia Bugzilla is closed!

Few problems here:

First of all, most PHP configurations limit the number of post parameters to 1000 (meaning one can only import 999 changes at time). It is possible to increase this number, but lets face it, it is hard to do and people will look grumpy changing settings made for security.

Another thing is you can only display about 10k changes at once, because of the time and memory needed to create the page. This is bug 37167.

One work around is to add limit to processMessageChanges, which stops after N changes, telling the user to import those first and then running the script again.

The first thing to fix would be to device work around for the 1000 post parameters limit, perhaps by adding paging for every 999 changes.