How many database instances are too much with the ezcomponents database component?

Question

Hi,

I want to connect to about 9 databases and create an instance for everyone of them to aggregate my results in the queries.

I am writing a metrics dashboard for my company that need to track results and performance over about 9 different databases with about 15mil+ records in each. Now the technical part is not hard. I know how to code it but I want to find out whats the best approach.

Theres option 1 : Create one database instance and do a UNION on all my select queries. (Note: All databases are on one box)

Option 2 : Create an instance for every database and separately query each one and aggregate the results.

This is more of a high level question if that helps.

Thanks!