You will find the old Database
FAQ for Moodle 1.9 at http://docs.moodle.org/19/en/Database_FAQ
(which I compiled some time ago). I haven't checked whether all the links are still valid (I fear not).
Unfortunately, the new cloning concept for Moodle Docs
(where each version gets its own wiki) - which IMHO
is already bad enough - doesn't extend to the Developer Documentation where you will only find information on the most current version of Moodle.
There are several threads in the Moodle Docs forum relating to that topic. The most recent one is "Performance docs in a mess"
. Please comment there if you want to change this pity state of Moodle Docs.