Coincidentally, one of the points I mentioned at the Hotsos Symposium was the increasing the sort_area_size could affect execution paths for the worse. (Even when there is no risk of excess memory usage causing swapping).
I was going to post a simple example to demonstrate this - and then cane across a really bizarre result in 8.1.7.4 and 9.2.0.2 - Using EXACTLY the same script to generate and report data, and hinting EXACTLY the same execution path, and running the 10053 trace against it, I built an example where the optimizer cost of sorting went UP when I increased the sort_area_size from 1M to 5M for a particular query. The 10053 trace showed: "cost / pass 18" when s_a_s was 1M, and " cost / pass 35" when s_a_s was 5M - when everything else was exactly the same. BTW - your statistics would suggest to me that I needed to find out what bits of code were doing so much sorting - and see if I could address the problem at source, rather than fiddling with database parameters. Regards Jonathan Lewis http://www.jlcomp.demon.co.uk Coming soon one-day tutorials: Cost Based Optimisation Trouble-shooting and Tuning Indexing Strategies (see http://www.jlcomp.demon.co.uk/tutorial.html ) ____UK_______March 19th ____USA_(FL)_May 2nd Next Seminar dates: (see http://www.jlcomp.demon.co.uk/seminar.html ) ____USA_(CA, TX)_August 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]> Date: 14 February 2003 17:54 hint >I changed my sort_area_size to 1M (down from 5M) and the query completed in 18 seconds. > >We had set sort_area_size to 5M at the suggestion of Oracle or other reasons. Looks like it's time to set it back. > >I ran the disk_sorts query and it returned this: > >DISK_SORTS AVERAGE_SIZE PEAK_CONCURRENT >---------- ------------ --------------- > 47073 23815K 826 > >Doesn't this suggest setting sort_area_size larger? > -- 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).
