The host has changed recently and the cursors are, apparently, incompatible with each
other, so we need to migrate to the new one, and this seems like the easiest way to
do it:
1. Store the host as part of the subscription state
2. Roll out the version that uses that new column as part of all queries
3. Switch to the new host
4. Roll out the version with the new host
- The new instance will start processing messages with a 0 cursor and so start anew
- The old instance will die off
This isn't a good way to do it though, because opreations processor is only called for each operation,
so we end up not updating the cursor as often as we realistically should be.
I'll refactor this slightly later
Aleksei Voronov