Oracle DBA RAC Interview Questions | Part - 1

1.What is cache fusion?

In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary).

2.What is split brain?

When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split brain.

3.What is the difference between Crash recovery and Instance recovery?

When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC environment the same recovery for an instance is performed by the surviving nodes called Instance recovery.

 4.What is the interconnect used for?

It is a private network which is used to ship data blocks from one instance to another for cache fusion. The physical data blocks as well as data dictionary blocks are shared across this interconnect.

5.How do you determine what protocol is being used for Interconnect traffic?

One of the ways is to look at the database alert log for the time period when the database was started up.

6.What methods are available to keep the time synchronized on all nodes in the cluster?

Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.

7.What files components in RAC must reside on shared storage?

Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.

8.Where does the Clusterware write when there is a network or Storage missed heartbeat?

The network ping failure is written in $CRS_HOME/log

9.How do you find out what OCR backups are available?

The ocrconfig -showbackup can be run to find out the automatic and manually run backups.

10.If your OCR is corrupted what options do have to resolve this?

You can use either the logical or the physical OCR backup copy to restore the Repository.

 

11.How do you find out what object has its blocks being shipped across the instance the most?

You can use the dba_hist_seg_stats.

12.What is a VIP in RAC use for?

The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.

13.How do we know which database instances are part of a RAC cluster?

You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.

14.What is OCLUMON used for in a cluster environment?

The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster related issues. It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.

15.What would be the possible performance impact in a cluster if a less powerful node (e.g. slower CPU’s) is added to the cluster?

All processing will show down to the CPU speed of the slowest server.