Oracle Memory Structure Explained

The main memory structures in Oracle database consist of SGA (System Global Area) and PGA (Program Global Area).

1. SGA is the shared memory area used by an Oracle database instance to store shared data and control information for the entire instance. The SGA mainly includes several components:
2. Shared Pool: stores the parsing results of SQL and PL/SQL, shared SQL area, shared cursors, and execution plans of shared SQL statements.
3. Buffer cache is an area used to store data blocks in order to reduce disk I/O operations.
4. Redo Log Buffer: Stores redo log information for transactions, used to restore database consistency.
5. Large Pool: A shared memory area used for storing large objects, such as buffers for sorting, backup operations, etc.
6. Java Pool: a memory area where Java classes and objects are stored.
7. PGA: The PGA is a private memory area used by each user process or session to store data and control information specific to that user or session. The main components of PGA include:
8. Sort Area: Memory area used for sorting operations.
9. Hash Area: Memory region utilized for hash join and hash group operations.
10. Session Memory: used to store variables and temporary result sets within the current session.

The design and management of these memory structures are crucial for the performance and stability of Oracle databases, requiring proper configuration and tuning to meet the needs of database applications.