The architecture of Oracle Database 19c

 The architecture of Oracle Database 19c 

1. Database Instance

A database instance consists of the Oracle software running on a server and the memory structures and background processes that manage the database.

Memory Structures

System Global Area (SGA): A shared memory region that contains data and control information for the Oracle database. Key components of the SGA include:

o Database Buffer Cache: Stores copies of data blocks read from the data files.

o Shared Pool: Caches SQL statements, PL/SQL code, and data dictionary information.

o Redo Log Buffer: Stores redo entries that contain a log of changes made to the database.

o Large Pool: Used for large memory allocations, such as backup and restore operations.

o Java Pool: Used for all session-specific Java code and data within the database.

o Streams Pool: Used by Oracle Streams for data replication and capture.

Program Global Area (PGA): A memory region that contains data and control information for a single server process or background process. The PGA is private to each process.

Background Processes

· Database Writer (DBWn): Writes modified blocks from the database buffer cache to the data files.

· Log Writer (LGWR): Writes redo log entries from the redo log buffer to the online redo log files.

· Checkpoint (CKPT): Signals DBWn to write data to disk and updates the control file and data file headers with checkpoint information.

· System Monitor (SMON): Performs crash recovery when the instance is started after a failure.

· Process Monitor (PMON): Cleans up failed user processes and releases resources.

· Archiver (ARCn): Copies redo log files to the archive location when they are full.

· Recoverer (RECO): Resolves distributed transaction failures.

· Shared Server (Snnn): Handles multiple user processes in a shared server environment.

· Queue Monitor (QMNn): Manages Oracle Streams and Advanced Queuing.

2. Physical Database Structures

The physical storage structures of an Oracle database include:

· Data Files: Store the actual data of the database.

· Control Files: Contain metadata about the database, including the structure of the database and the locations of data files.

· Redo Log Files: Store a log of changes made to the database to enable recovery in case of a failure.

· Archive Log Files: Copies of redo log files that can be used for media recovery and to keep a history of changes.

3. Logical Database Structures

Oracle organizes data into logical structures to facilitate data management and access:

· Tablespaces: Logical storage units that group related data files together. Each tablespace can contain multiple segments.

· Segments: Set of extents allocated for a specific logical storage structure, such as a table or index.

· Extents: Contiguous blocks of storage within a tablespace.

· Data Blocks: The smallest unit of storage in an Oracle database, corresponding to a specific number of bytes of physical database space on disk.

4. Data Access Structures

· Tables: Store data in rows and columns.

· Indexes: Provide fast access to rows in a table.

· Views: Virtual tables based on the results of a query.

· Synonyms: Aliases for database objects, providing a layer of abstraction.

5. Networking and Interoperability

· Oracle Net: The network layer that allows communication between the Oracle database and client applications. It handles connections, authentication, and data transfer.

6. Oracle Managed Files (OMF)

Oracle Managed Files simplifies database file management by automating the creation and deletion of database files. With OMF, the DBA specifies file system locations, and Oracle automatically names and manages the files.

7. Multitenant Architecture

Oracle 19c supports the multitenant architecture, which allows multiple pluggable databases (PDBs) to be managed within a single container database (CDB). This architecture provides efficient resource management and isolation of different databases while allowing them to share the same instance and infrastructure.

Summary

The architecture of Oracle Database 19c is designed to support efficient data management, high availability, and robust security. By understanding these key components and their interactions, DBAs can effectively manage and optimize their Oracle database environments.