Oracle Data Guard interview questions Part 1

 Here are some common Oracle Data Guard interview questions that could be asked during a job interview:

1. What is Oracle Data Guard?

• Answer: Oracle Data Guard is a disaster recovery and data protection solution for Oracle databases. It maintains one or more standby databases as copies of the production database. These standby databases can be used for failover, data protection, and offloading read-only query operations.

2. Explain the types of Standby Databases in Oracle Data Guard.

• Answer:
  • Physical Standby Database: A replica of the primary database, maintaining an exact binary copy. It can be opened in read-only mode for reporting purposes.
  • Logical Standby Database: A database that uses SQL to apply changes made to the primary database. It allows read-write operations, so it's more flexible than a physical standby.
  • Snapshot Standby Database: A physical standby database that can be opened for read-write activities temporarily while still maintaining its ability to apply logs from the primary database once it reverts to a physical standby.

3. What is the difference between synchronous and asynchronous Data Guard?

• Answer:
  • Synchronous Data Guard (Maximum Availability Mode): Data is written to both the primary and standby databases synchronously. This ensures no data loss, but there may be some performance overhead due to network latency.
  • Asynchronous Data Guard (Maximum Performance Mode): Redo logs are transmitted to the standby database asynchronously. The primary database does not wait for acknowledgment from the standby, which reduces performance impact but may allow data loss in case of a failure.

4. What are the different Data Guard protection modes?

• Answer:
  • Maximum Protection: Ensures no data loss by requiring that all redo log writes are completed on both the primary and standby before the commit is acknowledged.
  • Maximum Availability: Provides a balance between performance and data protection. It ensures data is replicated to the standby but allows for some performance trade-offs.
  • Maximum Performance: Focuses on minimizing the performance impact on the primary database by using asynchronous transmission.

5. What is a Data Guard Broker?

• Answer: Oracle Data Guard Broker is a management and automation tool for Data Guard configurations. It provides an easy-to-use interface for configuring, monitoring, and managing Data Guard. It helps automate failover and switchover operations, and simplifies the management of Data Guard environments.

6. What is a switchover operation in Data Guard?

• Answer: A switchover is a planned role reversal between the primary and standby databases, where the primary becomes the standby and vice versa. This operation allows maintenance to be performed on the primary database without data loss. It is often done for system upgrades or maintenance.

7. What is failover in Oracle Data Guard?

• Answer: Failover is the automatic or manual process of switching the role of the standby database to become the primary database in case of a failure of the primary database. This can occur without manual intervention, but it may result in some data loss if in asynchronous mode.

8. What is Data Guard log transport and log apply services?

• Answer:
  • Log Transport Services (LTS): Responsible for transporting redo data from the primary database to the standby database. It handles log file transfer.
  • Log Apply Services (LAS): Responsible for applying the redo logs received by the standby database. This ensures that the standby database is kept in sync with the primary.

9. How does Oracle Data Guard handle redo log transportation?

• Answer: Redo logs from the primary database are transmitted to the standby database using either synchronous or asynchronous modes. The transport is done over the network, and the logs are stored on the standby database’s archive log directory. The Data Guard can use features like Real-Time Apply to apply redo logs immediately after they are received.

10. What are some common troubleshooting steps in a Data Guard environment?

• Answer: Common troubleshooting steps include:
  • Checking the Data Guard configuration using dgmgrl.
  • Verifying network connectivity between primary and standby servers.
  • Reviewing the Data Guard logs and alert logs for errors.
  • Verifying that redo logs are being shipped from primary to standby.
  • Ensuring the correct application of redo logs on the standby database.
  • Checking the configuration of archive log destinations.
  • Ensuring that the standby database is not in a "MOUNTED" state for too long.

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