The new commer in Oracle memory architecture _Database Box).pdf

The new commer in Oracle memory architecture

1. 4 Understanding Oracle's Managed Global Area
(MGA): A New Chapter in Memory Architecture

Alireza Kamrani

While exploring Oracle's latest Al Database 26ai
documentation (Oracle Docs - Memory
Architecture Diagram), one feature that stands
out is the Managed Global Area (MGA) — a
modern evolution in Oracle’s memory design
that adds a new layer of flexibility and
intelligence.

What Is the Managed Global Area (MGA)?

The MGA (Managed Global Area) is a semi-
shared memory region that bridges the gap
between the System Global Area (SGA) and the
Program Global Area (PGA).

2. Unlike the SGA (which is fully shared across all
processes) or the PGA (which is private to a

single process), the MGA is shared selectively —
only among a trusted set of Oracle processes.
Its goal is to let certain background or
foreground processes share data and structures
dynamically, without the rigidity of static SGA
allocations.

The Power of “Namespaces” in MGA:

The key innovation behind MGA is its
namespace-based architecture that inherent
from Linux namespace concepts.

e Each namespace represents a logical
memory domain within the MGA — a kind of
“sandbox” or shared memory context that
related processes can attach to.

3. e These namespaces are modular and
dynamic — Oracle components can create,
attach, or drop them as needed.

+ For example, a namespace could be used
for:

+ A parallel query execution team sharing
intermediate results

+ A metadata caching group

+ A vector or Al operator needing temporary
shared state

+ Because each namespace is isolated, Oracle
can manage access, size, and cleanup
independently — keeping the system both
flexible and safe.

This namespace-based sharing allows Oracle to
optimize memory for on-demand collaboration
among processes, without the overhead or risk
of global sharing.

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Why Oracle Added MGA:

MGA fills an architectural gap between static
and private memory management:

+ Dynamic Sharing - Enables processes to
share temporary memory safely using
namespaces.

e Elastic 8 Modular - Memory segments can
be created, resized, or destroyed dynamically
— no instance restart required.

5. ¢ Controlled Scope - Only approved
processes can attach to a namespace; it's
not globally visible like the SGA.

+ Governed by PGA Limits - MGA usage
counts toward the PGA aggregate limit,
ensuring unified memory control.

+ Recoverable & Flexible - Enables better
resilience and cleaner memory lifecycle
management, especially for transient
workloads.

How MGA Fits in Oracle's Memory Hierarchy:

Here's how Oracle's three main memory areas
relate:

System Global Area (SGA)

Fully shared across the entire database instance.
Used for caches, buffer cache, and shared SQL
or library cache.

Mostly static — memory is allocated at instance
startup.

6. Program Global Area (PGA)

Private to each server or background process.
Used for sorts, session state, and runtime
working memory.

Dynamically allocated and freed per session or
process.

Managed Global Area (MGA)

Semi-shared — shared only among a trusted set
of Oracle processes.

Organized into namespaces, each acting as an
isolated memory domain.

Enables dynamic, temporary sharing of data
structures between related processes.

Elastic and modular — namespaces can be
created, resized, and dropped on demand.
Memory consumption is governed under PGA
aggregate limits for unified control.

Why This Matters for DBAs & Architects:
As Oracle continues to evolve toward Al-driven

workloads and adaptive memory management,
understanding MGA becomes essential:

7. e Monitor MGA memory usage within overall
PGA limits.

+ Expect more internal Oracle components
(e.g., vector search, Al operators, and parallel
processing) to leverage MGA namespaces
for optimized data sharing.

+ When tuning or troubleshooting, remember
that some shared structures may now live in
MGA namespaces rather than the SGA.

Finally, the Managed Global Area (MGA) brings
namespace-based intelligence and modularity to
Oracle's memory system.

It's not just shared memory; it's structured,
scoped, and smart memory — a foundation for
Oracle's next-generation database performance.

Alireza Kamrani

DATABASE
BOX