B木 - naoyaのはてなダイアリー
ので次は18章です。18章のHow b-tree database indexes work and how to tell if they are efficient (100' level) | mattfleming.com
A team member thought we should add an index on a 90 million row table to improve performance. The field on which he wanted to create this index had only four possible values. To which I replied that an index on a low cardinality field wasn't really going to help anything. My boss then asked me why wouldn't it help? I sputtered around for a response but ended up telling him that I'd get back to him with a reasonable explanation.
Imported from http://twitter.com/newsycombinator/status/2645303258 How b-tree database indexes work and how to tell if they are efficient http://bit.ly/dd6mf