Re: are hints still necessary in 9i?

Jonathan Lewis wrote:
> But how are Profiles different from Outlines ?

Profiles are a set of uber-statistics (and other additional information) that allow the optimizer to better optimize the particular SQL statement next time it sees it.

So for instance, correlations between different specific data values is something that may be stored in a profile (Make = 'Ford', Model="Taurus", for example).

Note that you typically can't collect them beforehand, because the possible permutations could get very high very quickly, and you opnly want to collect the ones that are actually used - so you really need a 'bad' SQL statement in your workload (or a set of SQL statement taht makes up a bounded tuning set) to identify that further analysis and optimization may be beneficial.

They are also not 'frozen' like an outline.

The cost discussion is interesting - the general belief is that capturing and comparing the performance automatically to identify the bad SQL statements (ADDM) is the cost, Profiles are the payback. Received on Thu Oct 09 2003 - 21:17:02 CDT