Which version are you on. I've just done a couple of simple checks on 11.2.0.3 and there doesn't seem to be any unreasonable conflict. Of course, if you specifiy table-level dynamic sampling and specify the single table cardinality for the same table then you have to expect one of the hints to "lose" - and in this case the cardinality hint overrides anything the dynamic sampling may have done. Regards Jonathan Lewis http://jonathanlewis.wordpress.com/all_postings Author: Oracle Core (Apress 2011) http://www.apress.com/9781430239543 ----- Original Message ----- From: <Christopher.Taylor2@xxxxxxxxxxxx> To: <oracle-l@xxxxxxxxxxxxx> Sent: Thursday, September 13, 2012 9:33 PM Subject: Fun with the CARDINALITY and DYNAMIC_SAMPLING hint | (Thanks to Jonathan Lewis, Greg Rahn (and others) I've been learning a lot about tweaking the execution paths for a particular problematic SQL. | A special thank you to you guys for all the blog posts (a tremendous source of knowledge) that you write at Oracle Scratchpad and StructuredData!) | I was playing around with the hints mentioned in the subject for a particular problematic query we're working on and using dynamic_sampling I could reduce the performance from 25M lios to 5M lios (which I think is still probably too high for this complex DSS query). | | However, when I added the CARDINALITY hint, it seems to immediately disallow the dynamic sampling hint (or something)? | | Anyone know if these 2 are compatible? It doesn't seem so. | | Also, as a "fun" learning experiment, I played around with cardinality hints that were completely unrealistic such as 9999999999 (9 billion) - interesting explain plans doing things like that :) Performance not so great, but was still interesting to see how you can move tables around in the xplan based on what you know of them. | | Chris | | -- //www.freelists.org/webpage/oracle-l