Performance comparison between Oracle singleinstance and RAC

[Former Member]

Hello folks,

I would ask if there is someone that has feedback about performance after migration from an Oracle single instance to Oracle RAC configuration.

There were gains on RAC or wait state introduced have generated slow down on performance?

Any help will be appreciate.

KIND REGARDS !!!!!!!!!!

Nicola

[stefan_koehler]

Hello Nicola,

we are not running SAP on Oracle RAC .. but maybe i can give you some input.

> There were gains on RAC or wait state introduced have generated slow down on performance?

The question is: What can slow down the SAP system in a RAC environment, when it runs fine on a single instance?

In general you need to take a closer look at your SQLs. In a RAC environment bad written SQLs are the "death" of your system. You will get a lot of block shipping / pinging (maybe an overloaded interconnect, etc.). Normally you need to think about other aspects too (like sequences, etc.), but a SAP system don't use this stuff.

In my experience the SAP SQLs are mostly written well in its context, but if you modify or write a lot of important code by your own, you should really investigate this. I heard a sentence some time ago, which describes it very well.

"If your application doesn't scale on a single instance - it will not scale on RAC"

So my suggestion: "Avoid logical I/O and you will have fun with SAP on Oracle RAC".

A first indicator is the value "Reads / User calls" in ST04.

(Quote: "If this value is greater than 30, this indicates expensive SQL statements")

http://help.sap.com/saphelp_sm32/helpdata/en/c4/3a7223505211d189550000e829fbbd/content.htm

Regards

Stefan