[wp-hackers] Meta tables: Take 5

[Otto]

On Thu, Aug 6, 2009 at 12:12 AM, Mike
Schinkel<mikeschinkel at newclarity.net> wrote:
> I'm not 100% sure I'm following you here.  Are you saying that MySQL creates
> a hash for string values in an index when there is only a small number of
> values making string values more efficient than they would otherwise be?

No, but if you only have a small number of values, then your b-tree
(or whatever structure it's using) never grows larger than that number
of values. This is irrelevant to the size of the index field (except
so far as you'd like all the values to fit into memory).

Fulltext indexes are different than normal indexes, mind you, but a
varchar does not have to be using a fulltext index.

> And if MySQL does do that, when does it stop hashing distinct string values?

It doesn't do any hashing, unless you explicitly specify for it to do
so (which can be done, I think, but I've never bothered). I don't see
why you'd have to do any hashing for the index to be small.

-Otto