Jochem, Can I just say that I sometimes stand in awe of you :)
Mark A. Kruger, CFG, MCSE www.cfwebtools.com www.necfug.com http://mkruger.cfwebtools.com -----Original Message----- From: Jochem van Dieten [mailto:[EMAIL PROTECTED] Sent: Friday, March 17, 2006 2:49 PM To: CF-Talk Subject: Re: Large count query > caching Aaron Rouse wrote: > What is a bitmap index? The short explanation: Most types of database index contain the value of the indexed field plus a pointer to the rest of the row. So if you are indexing a bigint, that is 8 bytes for the value, another 8 bytes for the pointer and some room for metadata. After alignment issues that means each tuple will be 20 bytes. The index for a table with N tuples with X distinct values will have a size of 20 N byte. A bitmap index is structured so that each tuple in the table costs only 1 bit, but has that price for each distict value. That means that the total index size will be X * N bit. For the long explanation check the manual of your database. Jochem ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Message: http://www.houseoffusion.com/lists.cfm/link=i:4:235687 Archives: http://www.houseoffusion.com/cf_lists/threads.cfm/4 Subscription: http://www.houseoffusion.com/lists.cfm/link=s:4 Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=89.70.4 Donations & Support: http://www.houseoffusion.com/tiny.cfm/54
