CBO

MERGE JOIN CARTESIAN: a join method or a join type?

By Franck Pachot . I'll present about join methods at POUG and DOAG. I'll show how the different join methods work in order to better understand them. The idea is to show Nested Loops, Hash Join, Sort Merge Join, Merge(…)

12cR2 Subquery Elimination

By Franck Pachot . More and more we can see crazy queries generated by ORM frameworks or BI query generators. They are build to be easily generated rather than being optimal. Then, the optimizer has to implement more and more(…)

CBO, FIRST_ROWS and VIEW misestimate

By Franck Pachot . There are several bugs with the optimizer in FIRST_ROWS mode. Here is one I encountered during a 10.2.0.4 to 12.2.0.1 migration when a view had an 'order by' in its definition.

Oracle 12cR2 : Optimizer Statistics Advisor

The Optimizer Statistics Advisor is a new Advisor in Oracle 12.2. The goal of this Advisor is to check the way you gather the statistics on your database, and depending on what is found, it will makes some recommendations(…)

CBO parse time – matching time with transformation

By Franck Pachot . By a strange coincidence, I've encountered several cases of long parse time recently. That was the occasion to give a closer look at a CBO trace enhancement that came with April 2016 PSU: Bug 16923858 Diagnostic(…)

OFE – Optimizer Features Enable

By Franck Pachot . Do you know the optimizer_features_enable parameter? What do you think about it? Good or bad to use it? If I tell you to set optimizer_features_enable parameter=11.2.0.4 when you upgrade to 12c, do you think it's a(…)