Top 60 Oracle Blogs

Recent comments


DDL invalidates your SQL right ?

I stumbled upon this post by optimizer guru Nigel Bayliss last week, so please have a read of that first before proceeding. But I wanted to show a simple demo of how management of cursors continues to improve with each version of the database.

Oracle 12cR2: exchange partition deferred invalidation

In a previous post I introduced the new 12cR2 feature where some DDL operations can use the same rolling invalidation than what is done with dbms_stats. On tables, DDL deferred invalidation is available only for operations on partitions. Here is how it works for partition exchange.

Here is my session environment:

SQL> whenever sqlerror exit failure
SQL> alter session set nls_date_format='hh24:mi:ss';
Session altered.
SQL> alter session set session_cached_cursors=0;
Session altered.
SQL> alter session set optimizer_dynamic_sampling=0;
Session altered.
SQL> alter system set "_optimizer_invalidation_period"=5;
System SET altered.
SQL> show user

Force Cursor Invalidation

Many times it occurs that an inappropriate execution plan is used which was produced by using the current values of bind variables provided at the time of the hard parse. But later on the variables change so much that another execution plan would be required. Unfortunately there is no automatism in 9i and 10g that would spot this fact. Oracle finally resolved this problem in 11g.

The trick is to virtually set the statistics for the object which is involved in the query. What I mean by virtually is that I read the current statistics and store the same statistics back what makes no harm but the side effect is that the cursor is invalidated and hence it will be re-parsed and hopefully this time optimized for the right values of bind variables.

Here is the code:

CREATE OR REPLACE PROCEDURE Invalidate_statistics (
p_ownname VARCHAR2,
p_tabname VARCHAR2
) IS