Oracle Real Application Cluster (RAC) Interview Questions - Part:2

1. When to use raw over CFS?

• Always when CFS is not available or not supported by Oracle.
• The performance is very, very important: Raw devices offer best performance without any intermediate layer between Oracle and the disk.

Note: Autoextend fails on raw devices if the space is exhausted. However the space could be added online if needed.

2. What CRS is?

Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments. In Release 2, Oracle has renamed this product to Oracle Clusterware.

3. What is VIP IP used for?

It returns a dead connection IMMIDIATELY, when its primary node fails. Without using VIP IP, the clients have to wait around 10 minutes to receive ORA-3113: “end of file on communications channel”. However, using Transparent Application Failover (TAF) could avoid ORA-3113.

4. Why we need to have configured SSH or RSH on the RAC nodes?

SSH (Secure Shell,10g+) or RSH (Remote Shell, 9i+) allows “oracle” UNIX account connecting to another RAC node and copy/ run commands as the local “oracle” UNIX account.

5. Is the SSH, RSH needed for normal RAC operations?

No. SSH or RSH are needed only for RAC, patch set installation and clustered database creation.

6. Do we have to have Oracle RDBMS on all nodes?

Each node of a cluster that is being used for a clustered database will typically have the RDBMS and RAC software loaded on it, but not actual data files (these need to be available via shared disk).

7. What are the restrictions on the SID with a RAC database? Is it limited to 5 characters?

The SID prefix in 10g Release 1 and prior versions was restricted to five characters by install/ config tools so that an ORACLE_SID of up to max of 5+3=8 characters can be supported in a RAC environment. The SID prefix is relaxed up to 8 characters in 10g Release 2, see bug 4024251 for more information.

8. Does Real Application Clusters support heterogeneous platforms?

The Real Application Clusters do not support heterogeneous platforms in the same cluster.

9. Are there any issues for the interconnect when sharing the same switch as the public network by using VLAN to separate the network?

RAC and Clusterware deployment best practices suggests that the interconnect (private connection) be deployed on a stand-alone, physically separate, dedicated switch. On big network the connections could be instable.

10. What is the Load Balancing Advisory?

To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag.

11. How many nodes are supported in a RAC Database?

With 10g Release 2, we support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database. Currently DBCA has a bug where it will not go beyond 63 instances. There is also a documentation bug for the max-instances parameter. With 10g Release 1 the Maximum is 63.

12. What is the Cluster Verification Utiltiy (cluvfy)?

The Cluster Verification Utility (CVU) is a validation tool that you can use to check all the important components that need to be verified at different stages of deployment in a RAC environment.

13. What versions of the database can I use the cluster verification utility (cluvfy) with?

The cluster verification utility is release with Oracle Database 10g Release 2 but can also be used with Oracle Database 10g Release 1.

14. If I am using Vendor Clusterware such as Veritas, IBM, Sun or HP, do I still need Oracle Clusterware to run Oracle RAC 10g?

Yes. When certified, you can use Vendor Clusterware however you must still install and use Oracle Clusterware for RAC. Best Practice is to leave Oracle Clusterware to manage RAC. For details see Metalink Note 332257.1 and for Veritas SFRAC Note 397460.1.

15. Is RAC on VMWare supported?

Yes. 

16. What is hangcheck timer used for ?

The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.

There are 2 key parameters for this module:

-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends setting it to 30seconds.

-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.

17. Is the hangcheck timer still needed with Oracle RAC 10g?

Yes.

18. What files can I put on Linux OCFS2?

For optimal performance, you should only put the following files on Linux OCFS2:

- Datafiles

- Control Files

- Redo Logs

- Archive Logs

- Shared Configuration File (OCR)

- Voting File

- SPFILE