SHARED POOL in ORACLE

In Oracle, the shared pool is a key component of the System Global Area (SGA), which is a memory area that is shared by all Oracle processes. The shared pool specifically is a region of the SGA that stores shared SQL and PL/SQL code, as well as other shared data structures that are used by Oracle server processes.

Here's an overview of the shared pool:

1. Purpose: The shared pool is primarily used to cache SQL and PL/SQL statements, parsed execution plans, and other frequently used data structures. By caching this information in memory, Oracle can avoid the overhead of re-parsing SQL statements and executing the same queries repeatedly.

2. Contents:

   • SQL and PL/SQL Statements: When a SQL or PL/SQL statement is executed for the first time, Oracle parses it, generates an execution plan, and stores the parsed representation in the shared pool. Subsequent executions of the same statement can reuse the parsed representation, saving parsing overhead.
   • Execution Plans: Oracle caches execution plans for SQL statements in the shared pool. This allows subsequent executions of the same SQL statement to reuse the same execution plan, improving performance.
   • Other Shared Data Structures: The shared pool also contains other shared data structures used by Oracle server processes, such as shared cursors, data dictionary information, and library cache.

3. Memory Management: The shared pool size is configurable and can be adjusted based on the system's requirements. You can control the size of the shared pool using the SHARED_POOL_SIZE initialization parameter in the initialization parameter file (init.ora or spfile.ora). Oracle automatically manages the contents of the shared pool, flushing least recently used (LRU) entries when additional memory is needed.

4. Performance Considerations:

   • Proper Sizing: It's important to size the shared pool appropriately to accommodate the workload of your Oracle database. Insufficient shared pool size can lead to frequent parsing of SQL statements and decreased performance.
   • Monitoring: Regular monitoring of shared pool utilization and performance metrics can help identify potential issues and tune the shared pool size accordingly.
   • Cursor Sharing: Oracle's cursor sharing feature allows similar SQL statements to share the same execution plan in the shared pool, reducing memory usage and improving performance.

Overall, the shared pool plays a crucial role in Oracle database performance by caching frequently used SQL and PL/SQL code and other shared data structures in memory.

Proper configuration and management of the shared pool are essential for optimizing database performance.