Instance Caging

Many of you would already be aware of this one while I discover it now but still putting down my thoughts on this 11g new feature.

Most of the times, we end up running multiple instances on a single box for developmental effort. Or even on Production by buying a reasonably big box to save on licensing cost and also in the name of consolidation exercise :). But doing so, throws up the challenge for a DBA in terms of allocating resources to each instance. Some low priority activity on an instance eating up CPU resources and thus depriving the much needed resource to those requiring it. CPU allocation decisions such as this are made solely by the operating system; the user generally has no control over them.

Instance caging in 11gR2 is a method to cage or bound the instance to use a certain no of CPU’s instead hogging all the available CPU’s. All we have to do is set an initialization parameter to control the CPU resources an instance can use. It basically limits the no of CPU’s an instance can use e.g. I can set this parameter to “1” on a 4 CPU machine. It’s very simple (silly :)) to set it –

ALTER SYSTEM SET CPU_COUNT = 4; 

However, it works with resource manager feature so you will need to enable RM and create a resource plan first before running the above command.

Instance caging can be useful on larger box with multiple instances running – some development and a few production allowing CPU and resource allocation be done effectively. Apart from this, it can also be said that it’s Oracle’s way (alternate option) of giving CPU resource allocation control to a DBA rather than leveraging a logical/physical partitioning of a large box resorting to usage of tools/technologies such as VMware, AIX LPAR or Sun containers etc. In a nut shell, it’s the simple way to control the CPU consumption of each database instance.

Maybe sometime later, I will try to post an example. Thanks for reading and appreciate your comments / thoughts.