11g vs Exadata- SQL Tuning approach

Question

We are developing an OLTP application in which the development database is in 11g and Production database would be in Exadata. We have a testing database in Exadata. The plan is to develop queries and tune it in 11g development database. After this, the tuned query would be run in testing Exadata database to ensure it works as expected. The assumption is that further tuning would not be needed in Exadata. I'm trying to see how big is the risk in making this assumption.
From a sql developer's perspective, how much different is the tuning approach between 11g & Exadata?
Edited by: museshad on Jun 7, 2011 12:47 PM
Edited by: museshad on Jun 7, 2011 12:51 PM

Answer 1

On a recent migration of an OLTP application we did have things that we had to look at. They were almost exclusively related to 10g to 11g upgrade issues though, with one notable exception. Although the application was 99% OLTP, there was an ETL type process that was run very frequently which depended on full table scans. It was not run using parallel query, but rather had many copies being run simultaneously in a do it yourself parallel fashion. Because the tables were relatively small, the serial direct path read mechanism was not being selected which eliminated all the Exadata Smart Scan optimizations. Long story short, getting Smart Scans to work on that portion of the application made a huge difference. So the point of the story is that it's rare to have "pure" OLTP that never does any full table scans. These are the areas where you should be expecting different behavior and thus focusing your testing. On the OLTP side you will want to do the same things you have done with pre-Exadata Oracle including avoiding as much I/O as possible via the buffer cache. The other thing to watch is to make sure when you are doing single block I/O that is making use of the Exadata Smart Flash Cache. I must say that I think the developers should have access to the platform where the application will live. Otherwise I don't know how you can expect them to learn what's possible and what to expect from the platform.
Kerry