Note in-line Regards Jonathan Lewis http://www.jlcomp.demon.co.uk The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html March 2004 Hotsos Symposium - The Burden of Proof Dynamic Sampling - an investigation March 2004 Charlotte OUG (www.cltoug.org) CBO Tutorial April 2004 Iceland June 2004 UK - Optimising Oracle Seminar ----- Original Message ----- From: "Mark Richard" <mrichard@xxxxxxxxxxxxxxxxx> > > I am unfortunately speaking from heresay, however I heard once that having > histograms all over the place can slow down parsing as they have to be > inspected. I was left with the impression that unless the data is skewed > enough to warrant a histogram then there actually is a negative cost > associated with having too many histograms. > I have to disagree with part of Wolfgang's comment. To use a histogram, Oracle has to load it into memory, then compare predicate values with end-points before producing a selectivity value. If you have histograms on every single column in the database, that's a lot of memory to load - and it seems to be protected by only one latch. The incremental CPU cost of using the histogram for any one optimisation call is probably not significant - but the infrastructure cost is. If you have a perfect system, that uses a few distinct thousand SQL statements, and optimises them just once, then the overhead is irrelevant. If you have a typical system, then it's another nail in the coffin. ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx put 'unsubscribe' in the subject line. -- Archives are at //www.freelists.org/archives/oracle-l/ FAQ is at //www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------