On T, 2004-10-26 at 18:42, Greg Stark wrote: > Hannu Krosing <[EMAIL PROTECTED]> writes: > > > I repeat here my earlier proposal of making the bitmap indexes > > page-level and clustering data automatically on AND of all defined > > bitmap indexes. > > The problem with page-level bitmaps is that they could be much less effective. > Consider a query like 'WHERE foo = ? AND bar = ? AND baz = ?" where each of > those matches about 1% of your tuples. If you have 100 tuples per page then > each of those bitmaps will find a tuple in about half the pages. So the > resulting AND will find about 1/8th of the pages as candidates. In reality the > number of pages it should have to fetch should be more like 1 in a million. > > The other problem is that for persist on-disk indexes they require more work > to update. You would have to recheck every other tuple in the page to > recalculate the bit value instead of just being able to flip one bit.
Read again ;) the per-page clustering would make sure that all the tuples would be on 1 (or on a few) pages. and what comes to updating the index, you have to do it only once per 100 pages ;) ---------------- Hannu ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
