Explain the Oracle database architecture.

• Discuss the major components such as the instance (SGA, PGA, background processes) and the database (datafiles, control files, redo log files).

What is an Oracle instance?

• Define an Oracle instance and describe its role in database operations.

What are the main components of an Oracle instance?

• Detail the System Global Area (SGA), Program Global Area (PGA), and the various background processes.

Describe the System Global Area (SGA) and its components.

• Explain components like the Database Buffer Cache, Shared Pool, Redo Log Buffer, Java Pool, Large Pool, and Streams Pool.

What is the Program Global Area (PGA)?

• Discuss the purpose of the PGA and how it differs from the SGA.

Explain the role of the Database Buffer Cache.

• Describe how the Database Buffer Cache works and its importance in Oracle architecture.

What is the Shared Pool?

• Discuss the purpose of the Shared Pool and its key components, such as the Library Cache and Data Dictionary Cache.

Describe the Library Cache and its function.

• Explain the role of the Library Cache in storing SQL execution plans and PL/SQL code.

What is the Data Dictionary Cache?

• Describe how the Data Dictionary Cache stores metadata information and its importance.

Explain the Redo Log Buffer and its purpose.

• Discuss how the Redo Log Buffer works and its role in transaction management and recovery.

What are redo log files, and why are they important?

• Explain the purpose of redo log files in maintaining data integrity and supporting recovery operations.

Describe the purpose of control files in Oracle.

• Discuss the critical information stored in control files and their role in database startup and recovery.

What is the parameter file (PFILE/SPFILE)?

• Explain the differences between PFILE and SPFILE and their roles in configuring Oracle instances.

Describe the structure of an Oracle database.

• Discuss datafiles, tablespaces, segments, extents, and data blocks.

What are tablespaces in Oracle?

• Explain the purpose of tablespaces and how they organize data storage.

Describe the different types of tablespaces.

• Discuss SYSTEM, SYSAUX, UNDO, TEMP, and user-defined tablespaces.

What is a datafile in Oracle?

• Explain how datafiles store database data and their association with tablespaces.

What are background processes in Oracle?

• List and describe the key background processes such as DBWn, LGWR, CKPT, SMON, PMON, and ARCn.

Explain the role of the DBWn process.

• Describe how the Database Writer process manages writing modified blocks from the SGA to the datafiles.

What does the LGWR process do?

• Discuss how the Log Writer process manages the writing of redo log entries from the Redo Log Buffer to the redo log files.

Describe the function of the CKPT process.

• Explain how the Checkpoint process ensures that all modified database buffers are written to the datafiles.

What is the SMON process?

• Discuss the System Monitor process and its role in instance recovery and cleanup of temporary segments.

What is the PMON process?

• Explain the Process Monitor process and its function in cleaning up failed user processes and releasing resources.

What is the ARCn process and why is it important?

• Describe the Archiver process and its role in copying redo log files to archive locations.

What is a control file backup?

• Explain why and how control files should be backed up regularly.

Explain the Oracle instance startup sequence.

• Describe the steps involved in starting up an Oracle instance (NOMOUNT, MOUNT, OPEN).

What are the different Oracle instance startup modes?

• Discuss the differences between NORMAL, IMMEDIATE, TRANSACTIONAL, and ABORT shutdown modes.

Describe the process architecture in Oracle.

• Explain user processes, server processes, and background processes.

What is a checkpoint in Oracle, and why is it important?

• Describe the purpose of checkpoints and their impact on database performance and recovery.

Explain SCN (System Change Number) and its significance.

• Discuss how SCNs are used in Oracle to maintain data consistency and support recovery operations.

What is a data block in Oracle?

• Describe the smallest unit of data storage in an Oracle database and how blocks are managed.

What is a segment in Oracle?

• Explain the different types of segments (table, index, undo) and how they organize data storage.

Describe the different types of segments in Oracle.

• Discuss table segments, index segments, temporary segments, and undo segments.

What is an extent in Oracle?

• Explain how extents are used to allocate space for segments and their role in database storage management.

How does Oracle allocate space for data?

• Discuss the process of allocating and deallocating extents and data blocks.