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/
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
