Notes in-line Regards
Jonathan Lewis http://www.jlcomp.demon.co.uk The educated person is not the person who can answer the questions, but the person who can question the answers -- T. Schick Jr One-day tutorials: http://www.jlcomp.demon.co.uk/tutorial.html Three-day seminar: see http://www.jlcomp.demon.co.uk/seminar.html ____UK___November The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html ----- Original Message ----- To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> Sent: Tuesday, December 02, 2003 9:04 AM > > A properly formed hint will cause the CBO to consider the hinted path to be > less costly than it would otherwise consider it, but hints do not force a > query to use that particular plan. Hints do not change the cost of a query - they simply dictate that Oracle should take the stated path and not consider alternatives which would otherwise be possible at that point in the plan. > For a moderately complicated query, > you'd potentially need a fair number of hints to get things working the way > you want. If the statistics of the table changed, though, your carefully > hinted query might well decide to take another path. Even if things work, > adding hints-- particularly adding multiple hints-- to a query > significantly increases the maintenance costs as future developers have to > unravel what all the hints are doing, why they're doing it, whether any > hints need to be changed as a result of the modifications, whether future > changes to the CBO or new Oracle functionality should cause the ideal plan > to change, etc. (a) One would hope that a hinted query would also have some documentation describing the expected execution plan, and the reaons why it was considered desirable - so the maintenance issues should be moot. (b) Plan stability exists to stop execution plans from changing - so any SQL with a plan should, by your comment above, require it's stored outline to be put under review in case any new functionality should be applied and the outline changed. So, again, your point is not entirely sound. > > If you want to force Oracle to use a particular plan, plan stability is > orders of magnitude easier! > Only if you happen to have the licence for the 9.2 performance tuning pack, and can use the dinky little GUI for drawing and manipulating outlines. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jonathan Lewis INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
