SQL Plan Management – Selective Automatic Plan Capture Now Available!

Over the years, Oracle has provided a number of techniques to help you control the execution plan for a SQL statement, such as Store Outlines and SQL Profiles but for me the only feature to truly give you plan stability is SQL Plan Management (SPM). It’s this true plan stability that has made me a big fan of SPM ever since it was introduced in Oracle Database 11g.

With SPM only known or accepted execution plans are used. That doesn’t mean Oracle won’t parse your SQL statements, it will. But before the execute plan generated at parse is used, we will confirm it is an accepted plan by comparing the PLAN_HASH_VALUE to that of the accepted plan. If they match, we go ahead and use that plan.

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Does the Explain Plan command really show the execution plan that will be used?

When it comes to SQL tuning we often need to look at the execution plan for a SQL statement to determine where the majority of the time is spent. But how we generate that execution plan can have a big impact on whether or not the plan we are looking at is really the plan that is used.

The two most common methods used to generate the execution plan for a SQL statement are:

EXPLAIN PLAN command – This displays an execution plan for a SQL statement without actually executing the statement.

V$SQL_PLAN A dynamic performance view introduced in Oracle 9i that shows the execution plan for a SQL statement that has been compiled into a cursor and stored in the cursor cache.

My preferred method is always to use V$SQL_PLAN (even though it requires the statement to at least begin executing) because under certain conditions the plan shown by the EXPLAIN PLAN command can be different from the plan that will actually be used when the query is executed.

So, what can cause the plans to differ?

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Getting the most out of Oracle SQL Monitor

I’m often asked what is the best tool for viewing execution plans and for me the answer is always SQL Monitor (included in the Oracle Tuning Pack). It really is the most invaluable tool if you need to determine what is happening during the execution of any long running SQL statements.

In order to help you get the very most out of using SQL Monitor, I wanted to share with you some of the tips and tricks I‘ve learnt over the years from the original Database Manageability team, especially Cecilia Grant!

So, why do I love it so much?

There are so many reasons to love SQL Monitor; it’s hard for me to know where to begin. So, instead of giving you an exhaustive list I’ve put together a short video to demonstrate how I use SQL Monitor (be sure to set your resolution to 720p).

How do I control what statements are monitored?

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