Re: plans for bitmap indexes?

Josh Berkus schrieb:
>>The most nearly comparable thing is be the notion of "partial
>>indexes," where, supposing you had 60 region codes (e.g. - 50 US
>>states, 10 Canadian provinces), you might set up indices thus:
> 
> I'm afraid that you're mistaken about the functionality of bitmap indexes.   
> The purpose of a bitmap index is not to partition an index, but to allow 
> multiple indexes to be used in the same operation.

uh. sorry! In my first harsh replay I didn't know that. I thought you 
wanted a new index type for binary images in BLOBS.
(just some hash, maybe optimized for image similarity)

> For example, imagine you have a table on a dating website with 18 columns 
> representing 18 different characteristics for matching.  Imagine that you 
> index each of those columns seperately. If you do:
> 
> SELECT * FROM people WHERE orientation = 'gay' AND gender = 'male' AND city = 
> 'San Francisco';
> 
> ... then the planner can use an index on orientation OR on gender OR on city, 
> but not all three.   Multicolumn indexes are no solution for this use case 
> because you'd have to create a multicolumn index for each possible combo of 
> two or three columns ( 18! ).   
> 
> The Bitmap index allows the query executor to use several indexes on the same 
> operation, comparing them and selecting rows where they "overlap" like a Venn 
> diagram.
-- 
Reini Urban
http://xarch.tu-graz.ac.at/home/rurban/