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Posted on Aug 26 • Edited on Sep 20

Understanding PRAGMA SERIALLY_REUSABLE in Oracle PL/SQL: A Complete Guide

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🔄 Understanding PRAGMA SERIALLY_REUSABLE in Oracle PL/SQL: A Complete Guide

PRAGMA SERIALLY_REUSABLE in Oracle PL/SQL

When working with Oracle PL/SQL packages, memory management and session state become crucial, especially in high-concurrency environments like web-based applications, batch processing systems, or shared server configurations. One powerful yet often overlooked feature for memory optimization is the PRAGMA SERIALLY_REUSABLE directive. This blog aims to break down this concept from scratch, providing both simple explanations and practical use cases for developers ranging from 5 to 15+ years of experience.

📘 What is PRAGMA SERIALLY_REUSABLE?

PRAGMA SERIALLY_REUSABLE is a PL/SQL compiler directive that tells Oracle not to retain global package variables between calls within the same session. In short:

🔹 Without pragma: Global variables persist for the entire session
🔹 With pragma: Global variables reset after each call, saving PGA memory

It is declared in both the package specification and package body, like so:

PRAGMA SERIALLY_REUSABLE;

🧠 Why Was This Introduced?

Oracle introduced this pragma to solve the problem of excessive PGA memory usage caused by persistent global states in packages, especially when the packages are used briefly and don’t need to retain data across session calls.

- In shared server environments (like Oracle’s MTS or web apps), session memory is stored in the User Global Area (UGA), and memory cleanup becomes crucial. Without the pragma, unused variables linger in memory, wasting resources.

📦 A Simple Package WITHOUT PRAGMA

CREATE OR REPLACE PACKAGE DemoPkg IS
PROCEDURE set_val(p_val NUMBER);
PROCEDURE get_val;
END DemoPkg;
/

CREATE OR REPLACE PACKAGE BODY DemoPkg IS
g_val NUMBER;

PROCEDURE set_val(p_val NUMBER) IS
BEGIN
g_val := p_val;
END;

PROCEDURE get_val IS
BEGIN
DBMS_OUTPUT.PUT_LINE('Value: ' || g_val);
END;
END DemoPkg;
/

🔎 Test Execution:

BEGIN
DemoPkg.set_val(99);
DemoPkg.get_val; -- Outputs: Value: 99
END;

Here, the variable g_val retains its value (99) between calls because it is globally persistent.

📦 Same Package WITH PRAGMA SERIALLY_REUSABLE

CREATE OR REPLACE PACKAGE DemoPkg IS
PRAGMA SERIALLY_REUSABLE;
PROCEDURE set_val(p_val NUMBER);
PROCEDURE get_val;
END DemoPkg;
/

CREATE OR REPLACE PACKAGE BODY DemoPkg IS
PRAGMA SERIALLY_REUSABLE;
g_val NUMBER;

PROCEDURE set_val(p_val NUMBER) IS
BEGIN
g_val := p_val;
END;

PROCEDURE get_val IS
BEGIN
DBMS_OUTPUT.PUT_LINE('Value: ' || g_val);
END;
END DemoPkg;
/

🔎 Test Execution:

BEGIN
DemoPkg.set_val(99);
DemoPkg.get_val; -- Outputs: Value: (NULL or empty)
END;

Because of the pragma, g_val is reset after set_val ends. So get_val sees no value assigned.

🔍 What’s Happening Behind the Scenes?

Oracle instantiates the package in UGA (User Global Area) rather than PGA
When the call finishes, the package memory is discarded
On the next call, the package is reloaded and reinitialized
Global variables don’t retain their values across calls
Improves memory efficiency at the cost of state persistence

✅ Where Should You Use It?

Use PRAGMA SERIALLY_REUSABLE when:
Your package has global variables used temporarily
You're building stateless modules like APIs, batch processes
You're operating in shared server or web app environments
You want to reduce PGA memory usage

❌ Where Should You Avoid It?

Avoid it when:
You need global state persistence across procedure calls
Your logic relies on maintaining session data
You're in dedicated server environments with abundant memory

🧑‍💼 Real-Time Example

Let’s say you have a package that performs temporary logging or counters in batch jobs. You don’t need to retain those counters after the procedure ends. Applying PRAGMA SERIALLY_REUSABLE here ensures those temporary values don’t bloat session memory—especially if many sessions are calling it simultaneously.

🔑 Keywords Summary

Keyword Meaning

PRAGMA SERIALLY_REUSABLE Oracle directive to discard global state after each call
Global Variable Declared in package body, persists unless pragma is applied
PGA Private memory for session-level data
UGA Shared memory when using shared server
Stateless Session A session where variables do not retain state

🏁 Final Thoughts

Using PRAGMA SERIALLY_REUSABLE is a smart choice when stateless, memory-efficient design is more important than maintaining global variables. Understanding how memory works behind the scenes (PGA vs UGA) and being deliberate about memory optimization is what separates senior developers from others.

Whether you’re building a large-scale enterprise app, a RESTful API, or a batch processor, this pragma can help you write scalable and efficient PL/SQL.

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