Tips on SQL Plan Management and Oracle Database In-Memory Part 1

If you follow Oracle’s In-Memory blog then you probably came across a post mentioning how you should use SQL Plan Management when you’re upgrading to Oracle Database In-Memory. Whether you have read that post or not, you might be wondering what will happen if you have some SQL plan baselines and you begin to populate the In-Memory column store with a bunch of tables as used by those baselines. That’s what this post is about. Well, in fact, I’m going to break the topic up into a few posts because (as ever!) there is a little bit of subtlety to cover. Luckily, this will make your life easier rather than more difficult because you can get immediate benefit from In-Memory even if you don’t evolve SQL plan baselines on day one.  

When I started to think about this post I thought that I would start with the first scenario that probably comes to mind if you’re familiar with SQL Plan Management (SPM): 

• The Optimizer comes up with a new execution plan for a SQL statement because something has changed, and Oracle Database In-Memory would be a very good example of that! 
• If there’s a SQL plan baseline for the statement, the database will use the baseline execution plan and capture the new plan.
• Where appropriate, the new plan will be validated and accepted using SQL plan evolution. 

I will get to that, but first it’s better to start with a couple of more subtle points. With this information in our back pocket it will be easier to understand (and explain) the more traditional aspects of SQL plan evolution in the context of Oracle Database In-Memory.

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