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[Oracle] Insights into SQL hints - Embedded global and local hints and how to use them

Introduction

The idea for this blog post started a few weeks ago when i had to troubleshoot some Oracle database / SQL performance issues at client site. The SQL itself included several views and so placing hints (for testing purpose) into the views was not possible, especially as the views were used widely and not only by the SQL with the performance issue. In consequence this blog post is about the difference between embedded global and local hints and how to use them.

 

[Oracle] DB Optimizer Part XI - Query transformation fixes false cardinality estimation with multiple OR predicates (in newer Oracle releases)

Introduction

This is a short blog post about another query transformation (check my first blog post [Oracle] DB Optimizer Part VIII - Looking under the hood of query transformation (done by CBO) with simple real life example first, if you never heard of the term "query transformations"), that fixes a cardinality estimation issue with multiple (OR) predicates that cover the whole data range. I have to admit that this is a special case, but it can happen as observed by my client