Donnerstag, 10. Oktober 2019

OGB Appreciation Day : manipulating execution plans

Tims call for OGB Appreciation Day 2019 (#ThanksOGB) comes in time this year.

Even unemployed at the moment, I had a chance to help a friend with some problematic SQL statements.

The statements are not that important at all but he possibilities we had to address the problems were great!

First of all an existing execution plan, together with session stats, ASH/AWR and in one case SQLTRACE. None of these sources of information shows all details we required, but all together provided sufficient information to understand the problem.
The probably most comprehensive way to get all these information (except tracing) is sqld360.

Next of course is the system of hints.
There are many discussions if hints are a good and bad thing. It's not me to argue it here.
I appreciate hints exist in Oracle RDBMS as they can be used if arguments in their favor are strong.

Third the possibilities to apply hints to a SQL are huge. Even the statement itself can not be changed, there are stored outlines, SQL Profile, SQL Plan Baselines in SQL Plan Management, SQL Patch, and if some really dirty tricks are required, SQL Translation Framework and other mean tools can be used.

So there are sufficient tools available to improve a statements execution.

The sheer amount of possibilities might be overwhelming or even deterrent. In fact it's not that complicated and results can be achieved in short time.
Writing this, it's always easy to deliver shiny fancy solutions when standing on giants shoulders.
To give some examples, here is a random selection of articles I used during the latest investigations:

Occurence - Jonathan Lewis
Fixing SQL Plans: The hard way – Part 1 - Advait Deo
SQL Profiles - Kerry Osborne
buffer sorts - Jonathan Lewis
Oracle’s OPT_ESTIMATE Hint: Usage Guide - Christo Kutrovsky
Visual SQL Tuning (VST) - Kyle Hailey

I'm grateful for the possibilities we have to fix SQL executions, and I'm also grateful for all those people who share their knowledge, so I can learn from them!

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