[Wikipedia-l] Re: Phase IV, Wikibooks.org/.com and WikimediaFoundation.org/.com (was Wikis and uniformity)

[Delirium]

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