Give all resources to a service/session/user

Question

Hi,
I'm looking for a way to let one user/session/service consume all availabe database resources. A short overview over our system: We've got a primary three node RAC and a physical standby database running on the same host using a different storage subsystem. The standby is primarily used for reporting purposes (active dataguard). We've got a software running that produces highly complex queries. There are about 100 such "datawarehouse" queries running at the same time taking a lot of physical and logical I/O. The problem: Sometimes we receive queries that have highest priority and which must be completed as fast as possible. But as you can imagine there is no chance of getting a fast result when there are 100 other queries running in the background all of which consume lots of I/O.
When I first came to this problem I thought of using the Resource manager. I would create a consumer group, give it about 95% of the resources in every resource plan and map it to a specific service which then can be used to issue critical queries. But when I decided to set this up I came across the documentation which told me that the resource manager only cares about CPU. There is no way to give the session 100% of all availible I/O. Then I read a posting in a forum which told "If there is no CPU for a session it cannot issue I/O requests. So restricting CPU access also restricts I/O". Ok, great.. But the problem is: The critical session will NEVER consume all available CPU power. And because of the Resource managers philosophy that it will only take action when a resource is at it's limit there will never be an restriction on cpu power.
My second approach was to quiesce the database, but that seems to require the sysdba privilege, which I will never give to any software. So my question is: Is there any way to solve this problem?
Many thanks in advance
Thomas

Answer 1

Hi,
since your are using Active Data Guard, which means you are on 11g, you should take a closer look on DBRM new features - switching plan based on the number of IO requests and active session pool constraints. If I understand your requirements correctly, you can switch your sessions which took too many IO to the constrained consumer group (either automatically or manually) and for that group you can set maximum number of active sessions. In this case, sessions which uses IO and should be constrained can be reduced in their number, which, I think, should reduce their IO needs in total.