100+ Oracle Database Administrator Interview Questions and Answers

Recovering deleted datafiles without backup

• Check if the datafiles are still in the operating system's recycle bin or trash folder

• Use data recovery software to scan the hard drive for deleted files

• If the above methods fail, try to recreate the datafiles using the CREATE DATAFILE command

• If the tablespace is still intact, use the RMAN RECOVER TABLESPACE command to recover the data

Upgrading to Oracle Database 19c and related challenges

• Ensure compatibility of existing applications with 19c

• Perform pre-upgrade tasks such as backup and patching

• Upgrade the database using DBUA or manual methods

• Address challenges such as deprecated features and changes in behavior

• Configure Data Guard for high availability and disaster recovery

• Rollback an OPatch using the -rollback option

• Use RMAN duplication to create a copy of the database for testing or reporting

Monitoring db performance using OEM AWR report

• Access OEM console and navigate to Performance tab

• Select AWR report option to generate a report

• Analyze the report for key performance metrics like CPU usage, memory utilization, I/O stats

• Identify any performance bottlenecks and take necessary actions to optimize db performance

Oracle architecture is a multi-tiered structure that includes the client, application server, and database server.

• Oracle architecture consists of multiple components such as the client, application server, and database server.

• The client sends requests to the application server, which in turn communicates with the database server.

• The database server manages the storage, retrieval, and manipulation of data.

• Oracle architecture follows a client-server model.

• The client can be a us...read more

Resolve gap on a Physical Standby in Dataguard by identifying the missing archived redo log files and manually copying them over.

• Check the alert log for errors related to missing archived redo log files

• Identify the sequence number of the missing redo log files

• Manually copy the missing archived redo log files from the primary database to the standby database location

• Register the missing redo log files using the ALTER DATABASE REGISTER LOGFILE command

To recover a deleted control file in Oracle Database, you can use a backup control file or create a new control file.

• If a backup control file is available, you can restore it using the RMAN utility.

• If a backup control file is not available, you can create a new control file using the CREATE CONTROLFILE statement.

• To create a new control file, you need to provide the necessary information about the database, such as datafiles, redo log files, and tablespaces.

• Once the control fi...read more

Cold backup is taken when the database is offline while hot backup is taken when the database is online.

• Cold backup is taken when the database is shut down and all files are copied to a backup location.

• Hot backup is taken while the database is still running and all files are copied to a backup location.

• Cold backup is slower and requires downtime while hot backup is faster and does not require downtime.

• Cold backup is more reliable as there is no chance of data being changed du...read more

Investigate the issue, analyze performance metrics, identify bottlenecks, optimize queries, and implement performance tuning.

• Investigate the issue by analyzing logs, monitoring tools, and gathering information from the client.

• Analyze performance metrics such as CPU usage, memory usage, disk I/O, and query execution times.

• Identify bottlenecks in the database system such as slow queries, inefficient indexing, or hardware limitations.

• Optimize queries by rewriting them, adding in...read more

A DBA is a database administrator who is responsible for managing and maintaining a company's database system.

• Roles include database design, security, backup and recovery, performance tuning, and troubleshooting

• Responsibilities include ensuring data integrity, availability, and accessibility

• Shift models vary depending on the company's needs, but may include on-call availability and rotating shifts

• Examples of database systems include Oracle, MySQL, and SQL Server

Checkpoint is a process in Oracle that writes dirty buffers from the buffer cache to data files.

• Checkpoint is triggered by various events like log switch, manual checkpoint, etc.

• It ensures that all committed data is written to disk and the database can be recovered in case of a crash.

• Checkpoint writes all dirty buffers from the buffer cache to data files.

• It also updates the control file and data file headers to indicate the most recent checkpoint.

• Checkpoint frequency can be c...read more

Oracle fetches data using the SQL engine and the buffer cache.

• When a select statement is executed, the SQL engine parses the statement and creates an execution plan.

• The execution plan is used to fetch data from the database.

• The buffer cache is used to store frequently accessed data in memory for faster access.

• Oracle uses a multiversion read consistency model to ensure that data is consistent.

• Data is fetched in blocks called database blocks, which are stored on disk.

• Oracle use...read more

Maintaining the database involves regular monitoring, performance tuning, applying patches, and ensuring backups are taken regularly.

• Regularly monitor database performance and usage

• Perform routine maintenance tasks such as applying patches and updates

• Take regular backups to ensure data integrity and disaster recovery

• Implement security measures to protect the database from unauthorized access

• Optimize database performance by tuning queries and indexes

Monitor performance metrics and analyze execution plans to identify slow SQL queries without user interaction.

• Check the database performance views like V$SQL and V$SESSION to identify long-running queries.

• Use AWR (Automatic Workload Repository) reports to analyze historical performance data and identify trends.

• Examine the execution plan of the SQL query using EXPLAIN PLAN to identify potential bottlenecks.

• Look for high resource-consuming queries by checking CPU and I/O statis...read more

To check long running in database, use SQL queries to identify and troubleshoot slow queries.

• Use Oracle Enterprise Manager to monitor database performance

• Check the V$SESSION_LONGOPS view to identify long running operations

• Use SQL trace to identify slow queries

• Check the alert log for any errors or warnings

• Use AWR reports to analyze database performance over time

DataGuard installation involves configuring primary and standby databases for data protection and disaster recovery.

• Configure primary database for archiving redo logs

• Configure standby database for receiving redo logs from primary

• Set up DataGuard broker for managing the configuration

• Monitor DataGuard performance and synchronization

• Test failover and switchover scenarios for disaster recovery

Background processes are essential components of Oracle database that run continuously in the background. Memory architecture is the way Oracle manages memory.

• Background processes include DBWn, LGWR, PMON, SMON, etc.

• Memory architecture includes SGA, PGA, buffer cache, shared pool, etc.

• SGA is a shared memory region that stores data and control information.

• PGA is a private memory region that stores session-specific information.

• Buffer cache is a portion of SGA that stores data b...read more

Up to 60 nodes can be implemented in RAC.

• RAC stands for Real Application Clusters

• The number of nodes depends on the version of Oracle Database being used

• Oracle Database 12c supports up to 60 nodes in RAC

To create a schema, use CREATE SCHEMA statement. Data types include VARCHAR2, NUMBER, DATE, etc.

• Create a schema using CREATE SCHEMA statement

• Specify data types for columns when creating tables

• Common data types include VARCHAR2, NUMBER, DATE, etc.

• Use appropriate data types based on the type of data being stored

To patch specific db components to reduce downtime, follow these steps:

• Identify the specific components that need to be patched

• Plan the patching process during a scheduled maintenance window

• Backup the database before applying patches

• Apply patches to the specific components one by one

• Test the patched components to ensure they are functioning correctly

• Monitor the database for any issues post-patching

A database is a collection of related data, while an instance is the set of memory structures and background processes used to access the database.

• Database is the physical or logical container for data, while instance is the set of processes and memory structures used to access the database.

• Multiple instances can access the same database, but each instance has its own memory and processes.

• Database is persistent, while instance is transient and can be started or stopped.

• Exampl...read more

Physical stand-by is a standby database that is an exact replica of the primary database, while snapshot standby is a read-only standby database that allows for testing and reporting.

• Physical stand-by is an exact replica of the primary database, maintained through redo apply.

• Snapshot standby is a read-only standby database that allows for testing and reporting.

• Snapshot standby can be converted back to a physical stand-by database if needed.

New version has improved security, performance and automation features.

• Improved security with new encryption algorithms and secure password management

• Enhanced performance with in-memory column store and advanced indexing

• Automation features like automatic data optimization and automatic storage management

• New features for database management like JSON support and sharding

• Cloud integration with Oracle Cloud Infrastructure and Autonomous Database

Oracle database is a relational database management system developed by Oracle Corporation.

• It is a software system used to manage and store data.

• It uses Structured Query Language (SQL) to manage data.

• It is widely used in enterprise applications.

• It provides features like data security, backup and recovery, and scalability.

• Examples of Oracle database applications include online banking systems, airline reservation systems, and e-commerce websites.

To take RMAN backup quickly, use parallelism, compression, and backup sets.

• Use multiple channels to take backup in parallel

• Enable compression to reduce backup size

• Use backup sets to split backup into smaller pieces

• Use incremental backup to reduce backup time

• Use fast recovery area to store backups for quick recovery

11i and R12 are two different versions of Oracle E-Business Suite.

• 11i is the older version, released in 2000, while R12 was released in 2007.

• R12 has a more modern architecture and improved features, such as online patching and subledger accounting.

• Upgrading from 11i to R12 requires careful planning and testing.

• Both versions are still in use, but Oracle has announced that support for 11i will end in 2020.

TNS is a network protocol used to connect to Oracle databases, while LISTENER is a process that listens for incoming connection requests.

• TNS (Transparent Network Substrate) is a protocol used to establish connections between clients and Oracle databases.

• LISTENER is a process that runs on the database server and listens for incoming connection requests.

• TNS resolves the service name to the database's network address, allowing clients to connect.

• LISTENER receives connection requ...read more

Oracle is a relational database management system developed by Oracle Corporation.

• Oracle is used to store and manage data in a structured manner.

• It supports SQL and PL/SQL programming languages.

• Indexes are updated by the database itself as part of its maintenance tasks.

• However, DBAs can also manually update indexes if needed.