Mastering Memory Management in Oracle Database 23c: An Overview of Unified Memory Management

 Memory management in Oracle Database is a critical aspect that influences the efficiency and performance of database operations. In Oracle Database, two primary memory structures—System Global Area (SGA) and Program Global Area (PGA)—need to be managed effectively. Oracle offers several methods for memory management, which can be configured through initialization parameters.

Unified Memory Management: A New Era

Oracle Database 23c introduces Unified Memory Management (UMM), a modern approach designed to simplify and enhance memory management. This method is a significant advancement over previous techniques, integrating and improving upon Automatic Memory Management (AMM) with a single, streamlined parameter: MEMORY_SIZE.

Key Features of Unified Memory Management:

• Single Parameter Configuration: With UMM, you configure memory using a single parameter, MEMORY_SIZE. This parameter allows the database to manage memory dynamically, allocating resources among SGA, PGA, and other segments based on the total memory size you specify.
• Dynamic Allocation: UMM dynamically adjusts the allocation of memory between different segments such as SGA, PGA, and others, depending on the workload and the size of the Pluggable Databases (PDBs) in the Container Database (CDB).
• Support for Huge Pages: When configured, huge pages can be utilized for both SGA and PGA, potentially boosting performance by improving memory efficiency.

Automatic Memory Management: Efficient but Limited

Before the advent of UMM, Automatic Memory Management (AMM) was the recommended approach for managing memory. AMM automates the adjustment of memory between SGA and PGA based on workload demands. However, it is most effective for databases with a total SGA and PGA memory of 4 GB or less.

Benefits of Automatic Memory Management:

• Dynamic Adjustment: Automatically adjusts memory allocation between SGA and PGA to meet processing needs.
• Simplicity: Requires only the specification of total memory size, with Oracle handling the rest.

Manual Memory Management: For the Hands-On DBA

For those who prefer a more granular control over memory allocation, Manual Memory Management offers several methods. These can be used for both SGA and PGA, and they vary in complexity and automation:

• Automatic Shared Memory Management: For managing SGA.
• Manual Shared Memory Management: For more precise control over SGA.
• Automatic and Manual PGA Memory Management: For managing instance PGA.

When to Use Manual Memory Management:

• Complex Configurations: When detailed control is needed over individual memory components.
• Advanced Performance Tuning: When specific configurations are required to optimize performance.

MEMORY_SIZE in Oracle Database 23c

The introduction of MEMORY_SIZE in Oracle Database 23c represents a leap forward in memory management. This parameter:

• Specifies Instance-Wide Memory: Sets the total memory available for the database instance.
• Supersedes Old Parameters: Replaces the need for MEMORY_TARGET and MEMORY_MAX_TARGET, simplifying configuration.
• Dynamic Modifications: Allows for dynamic adjustments post-instance startup, provided the value does not exceed MEMORY_MAX_SIZE.

Notable Points:

• Range of Values: MEMORY_SIZE can be set between 1536 MB and MEMORY_MAX_SIZE.
• Impact on SGA and PGA: Internally calculates sizes for SGA_TARGET and PGA_AGGREGATE_LIMIT based on the MEMORY_SIZE.

In summary, Oracle Database 23c's Unified Memory Management offers a more flexible and efficient way to handle memory, building on the strengths of previous methods while introducing new features for enhanced performance. Whether you're transitioning from AMM or exploring manual configurations, UMM provides a modern solution to meet today’s demanding database environments.

Explore Unified Memory Management in Oracle Database 23c and see how it can optimize your database operations.