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Wednesday, March 4, 2009

Oracle BI High Availability: Part 3

The following is the third installment on the topic of High Availability within an OBIEE environment. As I mentioned in previous posts, much of what I’ll be discussing was covered in an Oracle eSeminar which I recently viewed on the subject. To quickly summarize, our basic goal within an HA implementation is to provide multiple instances of all components from the BI Server all the way to the end user, so if anything fails, we have another instance of the same component ready to go. The first two posts on the subject can be found in the blog archives if you’d like to rewind. This installment will feature the HA connections between the Presentation Servers and BI Scheduler Servers as well as between the Presentation Servers and BI Servers. We’ll also look closer at the BI Scheduler Cluster configuration.

First we’ll look at the connection between the BI Servers and the Presentation Servers. This again is handled by the Cluster Controller. In a Windows environment you’ll need to go into the Administrative Tools on each Presentation Server and set up the clustered ODBC data source. To do so, simply ensure that “Is this a clustered DSN?” is checked, then specify the primary and secondary cluster controllers and ports. On a Unix/Linux box, you’ll need to make the following changes to the odbc.ini file:






One important note to keep in mind is that if you have any clients from which you want to access your repository in online mode, you’ll need the clustered DSN set up on these as well. They’ll need the same connection to the BI Servers as the Presentation Servers will.

The BI Scheduler Cluster Controller assigns the active Scheduler server. In an HA environment, you would have two cluster controllers, a primary and a secondary, in an active/passive relationship. The secondary server will not be used unless the primary is unavailable. The client Controller ports are specified in the respective NQClusterConfig.INI files. The Scheduler configuration will be handled by the Cluster Controllers, so all we need to do in the instanceconfig.xml file is point to the Cluster Controllers, as shown below:



ccsPrimary=”<Primary Cluster Controller>

ccsPrimaryPort=”<Client Controller Port>

ccsSecondary=”<Secondary Cluster Controller>

ccsSecondaryPort=”<Client Controller Port>



The other task you would need to complete is to add the BI Scheduler Administrator credentials to the credential store of each ps. The quickest and easiest way would probably be to copy the credential store file from one instance to all other presentation servers.

A few notes about what will occur when the Active Scheduler fails. The transition from one server to another is seamless to the user’s perspective. The users won’t receive any errors, the Cluster Controller will simply detect the failure on the active server and point to the secondary. Any jobs which didn’t complete will be picked up where they left off. One important note to remember is that once the primary server is back up, it will not automatically resume the primary role. Only after the services have been restarted will the primary Scheduler resume its proper role. If any Java, command line, or script jobs are being run during an interruption, they will be restarted when another server is activated and given a new job ID. Take a look at the diagram of the basic HA architecture for the Scheduler Servers.

To configure the Cluster Controller to talk with multiple Schedulers, you must make the following entry in the NQSClusterConfig.INI file on each Cluster Controller:

SCHEDULERS = "scheduler1:9705:9708", "scheduler2:9705:9708";

The first port number for each scheduler will be the rpc port, where the Scheduler will be listening for connections from the Scheduler. The second will be the monitor port, which simply listens for a “heartbeat” from the Scheduler, to confirm it’s still available. This is how the Cluster Controller determines that the primary server has gone down and it needs to look to the secondary server. The default ports for the rpc and monitor ports are 9705 and 9708, respectively.

Configuration of the BI Scheduler Servers themselves can be completed through the Job Manager or via command line using schconfig. All configuration settings are saved in the instanceconfig.xml file of the Scheduler folder, not to be confused with the file of the same name in the web\config folder. The Scheduler can be configured to talk with multiple Presentation Servers and Java Hosts, which will be necessary if you are setting up a true HA environment. If you are using the Scheduler to run script files, you must place them in a shared network file, so that multiple Scheduler Servers can access them. All Schedulers should have read/write access to these files.

That’s going to wrap it up for this post. I’ll finish things up next time with a closer look at the BI Server cluster and how it’s integrated into the HA environment.