Timwi wrote:
I have asked my friend and he confirmed by suspicion.
If you have several large tables A, B, C, ... etc. with identical columns and types (that could, for example, be the recentchanges tables for the different languages), you can always combine them into a big table with an extra (indexed) integer or other fixed-length column that specifies what original table the row came from (i.e. what language it's in), and it won't be any slower.
This is true in theory, and I believe true in some "big iron" production database systems (Oracle, etc.), but I'm not sure it's true in practice in many of the free DB systems. In particular, big tables and big indexes can mess up caching algorithms. In fact sometimes it seems to even be beneficial to split into entirely separate databases (not just separate tables in the same database). Why this is true I don't know enough about the internals of the various DB systems to say, but splitting seems to have resulted in a large speedup at kuro5hin.org, among other places that use MySQL.
-Mark