Database tweaking for better performance

Working on the performance issues mentioned a few days ago. First of all, we reduced the overall table size by splitting one big table into smaller pieces. Roughly said, we now have now tables for North America, Europe, Asia, South America, Africa and the Pacific/Australia.

That worked well but still, some queries took longer than we think a query should take. Another idea was to shrink both, the whole SQL query and the rows a query must pass through. Therefore we converted the index relevant double values to integers. The result is, that the query is a bit shorter. The query is not as accurate as the double version, but the overall query time is now acceptable for this iteration. What's more important: we have a scalable approach if we need to speed up the queries.