On Sat, Jan 29, 2005 at 01:56:12PM +0200, Victor Y. Yegorov wrote: > 2) Queries, like "where A = 1" or "where A != 2" will require only 1 scan of > the index, while "where A < 3" will require 2 stages: 1st create a > list of > values lesser then 3, 2nd --- do OR of all bitmaps for that values. > For high cardinality attributes, this can take a lot of time; > > 3) Each bitmap is only a bitmap, so there should be an array of > corresponding > ctids pointers. Maybe, some more arrays (pages, don't know). > > For 2)nd --- there are techniques, allowing better performance for "A < 3" > queries via increased storage space (see here for details: > http://delab.csd.auth.gr/papers/ADBIS03mmnm.pdf) and increased reaction time > for simple queries. I don't know, if they should be implemented, may later.
Sorry if this is in the PDF but I didn't want to read 17 pages to find out... for the example where 1 >= A >= 4, couldn't you just do NOT (A >= 3)? Granted, in this example it wouldn't matter, but it would be faster to do this if you asked for A < 4. One downside is that you'd also have to consider the NULL bitmap, if the field is nullable. -- Jim C. Nasby, Database Consultant [EMAIL PROTECTED] Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?" ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
