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Wednesday, January 21, 2009

Oracle BI High Availability: Part 2

This is the second installment in a series of posts in which I’ve been discussing the implementation of High Availability within an OBIEE environment. Much of what we’ll be discussing was in included in an Oracle eSeminar which I recently viewed on the topic. In my original post, I gave the broad strokes in regards to HA and provided the basic overall architecture of a High Availability deployment. This time, we’ll start to dive into some of the specifics regarding configuration which will be necessary to implement a true “shared nothing” HA environment.

Each Presentation Server can be configured to talk with multiple web servers, Java hosts, BI Servers, and BI Schedulers. In this installment we’ll cover the Presentation Catalog, web server, and Java host connections to the Presentation Servers as well as how the user is affected when a Presentation Server fails. The diagram below is a subset of the one shown in my original post on the subject. This figure shows only the components of the HA architecture which we’ll be looking at today.

First, let’s discuss the web client behavior in a High Availability environment. When a user begins a session, the web client is bound to a specific Presentation Service and subsequent requests will be sent to that same service. When a Presentation Service failure occurs, the error is relayed back to the browser and any unsaved data will be lost. Upon logging in again, the user will be bound to another available Presentation Service. Two exceptions to this rule would be if the user is using SSO or if the Presentation Services plug-in is configured to automatically reconnect to another server. In these cases, there may still be a loss of session state. There will also be a time lag to recognize the failed server. This lag will be dependent on plug-in ping settings which we’ll get to eventually.

Any iBots which fail to complete as a result of a Presentation Service failure will result in an error being passed to the BI Scheduler Server and will be included in the log file. When the next available Presentation Service becomes available, the job is rerun without impact and will start again at the step in which it originally failed.

Next, we’ll look at how we would like our Presentation Services to share the Presentation Catalog. There are two basic options which can be deployed. The first option is to use a shared file system. All presentation servers have access to the same shared files. This is the simplest approach and, as I mentioned in my last post, is recommended by Oracle. Alternatively, a more complex method of catalog replication can be deployed through the use of replication agents on each instance which will monitor a single instance for changes and sync other copies as necessary. Two-way replication, which involves making changes to multiple copies of the Presentation Catalog and attempting to keep them all in sync, is highly discouraged and should be avoided. As you can imagine, this method would make maintaining data integrity much more difficult and complicated.

If you’ll be using the shared file approach, the first step necessary will be to point each presentation server to the shared file path by editing the <Catalog> element of the instanceconfig.xml file. In addition, we should also make changes the Presentation Service cache settings. Keep in mind that each instance will have its own cache, which we’ll want to configure to ensure it won’t get stale. Oracle recommends adding the following settings to each configuration file:


<ReportIndexRefreshSecs>120 </ReportIndexRefreshSecs>

<AccountCacheTimeoutSecs>180 </AccountCacheTimeoutSecs>

<PrivilegeCacheTimeoutSecs>180 </PrivilegeCacheTimeoutSecs>




Another piece of the puzzle will be to configure the presentation servers to work with multiple Java hosts. Once again, we must edit instanceconfig.xml to complete this task. This will involve listing the java host instances as shown below. The default Java Host port is 9810, but you can verify this by checking the OracleBI_Home\web\javahost\config\config.xml file. Simple load balancing will be performed in a round robin fashion between all instances listed in the config file.



<Host address=”<Javahost Machine1>” port=”9810”/>

<Host address=”<Javahost Machine2>” port=”9810”/>



You may also add an optional LoadBalance/Ping element. This element specifies the criteria for determining whether a Java Host is reachable. The ping element is not necessary if you wish to keep the default, which is 5 pings at 20 second intervals.

The final component we’ll look at today is the BI pres Services plug-in, which sits on the web servers. Here I’ll outline the changes necessary on each web server instance both for IIS and Java-based servers. IIS web servers will use the ISAPI plug-in, and the config file for this plug-in can be found in the OracleBIData_Home\web\config directory. The only element you must configure is the Hosts element, in which you will list the host and port of all Presentation Service instances. You may also optionally configure the LoadBalancer element which controls the autoroute feature. The default setting is false, which means that the user will receive an error if the current Presentation Server goes down. Setting this option to true would cause the server to attempt to connect to the next available Presentation Server without impact to the user. You also have the option of adding the ping element, which is the same element we just discussed when examining the Java host configuration.

The Java Servlet changes necessary for Java-based web server configuration are very similar to the ISAPI configuration mentioned above. You’ll need to edit the config file found in the OracleBI_Home\web\app\WEB-INF directory to include all Presentation Server host and port pairs. The <> element is equivalent to the <LoadBalancer> element with the ISAPI plug-in and should be set to “Y” or “N”.

Next time we’ll continue to discuss the BI Presentation Server and how it will be configured to talk with the BI Server and Scheduler…