How to Read a SQL Execution Plan in Oracle – Free Tutorial
Duration: 14 minutes
Reading Execution Plans is a Required Prerequisite to SQL Tuning!
In this free tutorial you will learn how to generate and read (i.e. interpret) an execution plan in Oracle Databases.
Understanding what the Oracle Database does with your SQL is essential to tuning – and the execution plan is the key.
Oracle Certified Master DBA John Watson will provide a brief introduction (4 minutes) – which includes John’s tuning methodology, then demonstrate EXPLAIN PLAN, SQL*Plus AUTOTRACE and DBMS_XPLAN.DISPLAY_CURSOR. In the demonstration, John will teach you:
• How to read an execution plan
• Find the 1st step in the plan
• Decipher the order of the steps in the plan
• That EXPLAIN PLAN can be very misleading
Prerequisites: To get the most from this tutorial, you should:
• Know how to code SQL
• Be familiar with SQL*Plus
• Know – in very general terms – what an execution plan is.
• Have a basic understanding of the Library Cache (this is where Oracle Database stores parsed SQL statements)
• Have a basic understanding of the Cost Based Optimizer (this is the part of the database that parses your SQL, creates an execution plan. Hopefully the correct – most efficient – plan).
Next Step: 12c Adaptive Execution Plans and 12c Re-Optimization of Execution Plans
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