Oracle PLAN_TABLE Setup and EXPLAIN PLAN Usage Guide

calendar Jun 29, 2025 / · 4 min read · oracle database sql performance optimization explain-plan query-tuning dba  ·
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What is the Oracle PLAN_TABLE and how do you use it?

Oracle's PLAN_TABLE is a fundamental component for SQL performance analysis and query optimization. This comprehensive guide explores the setup, usage, and best practices for leveraging Oracle's execution plan functionality to optimize database performance.

SQL Code

1@?/rdbms/admin/utlxplan.sql

Understanding The Oracle PLAN_TABLE

The PLAN_TABLE serves as the default output repository for Oracle's EXPLAIN PLAN statement, storing detailed information about how the database optimizer intends to execute SQL queries.

Oracle Database automatically creates a global temporary table called PLAN_TABLE$ in the SYS schema and establishes PLAN_TABLE as a synonym, ensuring every session receives its own private copy in the temporary tablespace.

Key Benefits of PLAN_TABLE:

  • Query Analysis: Reveals execution strategies without actually running queries
  • Performance Optimization: Identifies bottlenecks and inefficient operations
  • Cost-Based Insights: Shows optimizer decisions and resource estimates
  • Debugging Tool: Helps troubleshoot slow-performing SQL statements

Setting Up PLAN_TABLE with utlxplan.sql

Automatic vs Manual Setup

While Oracle automatically provisions PLAN_TABLE for users, you can manually create a local version using the utlxplan.sql script. This script is typically located in the $ORACLE_HOME/rdbms/admin directory on Unix and Linux systems.

Manual Creation Process

1-- Connect with appropriate privileges 
2CONN sys/password AS SYSDBA  
3-- Execute the utlxplan.sql script 
4@$ORACLE_HOME/rdbms/admin/utlxplan.sql  
5-- Create public synonym (if needed) 
6CREATE PUBLIC SYNONYM plan_table FOR sys.plan_table;  
7-- Grant necessary privileges 
8GRANT ALL ON sys.plan_table TO public;

EXPLAIN PLAN Functionality and Usage

Basic EXPLAIN PLAN Syntax

1-- Basic EXPLAIN PLAN usage 
2EXPLAIN PLAN FOR SELECT e.employee_name, d.department_name FROM employees e JOIN departments d ON e.department_id = d.department_id WHERE e.salary > 50000; -- Display the execution plan 
3SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());

EXPLAIN PLAN Limitations

Oracle imposes certain restrictions on EXPLAIN PLAN functionality:

  • Bind Variable Limitations: Cannot determine bind variable types, assuming VARCHAR by default
  • Implicit Type Conversion: Not supported for date bind variables
  • Execution Variance: Actual execution may differ from planned execution due to runtime conditions

DBMS_XPLAN Package for Plan Display

Display Functions and Options

The DBMS_XPLAN package provides sophisticated formatting options for execution plan output. Key display functions include various detail levels:

Format Options:

  • BASIC: Minimal plan information
  • SERIAL: Standard serial processing details
  • TYPICAL: Comprehensive plan with statistics
  • ALL: Complete plan with all available information
1-- Different DBMS_XPLAN display options 
2SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY()); 
3SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY('MY_PLAN_TABLE', 'st1','TYPICAL'));

Utility Scripts for Plan Display

Oracle provides specialized scripts for different execution scenarios:

  • utlxpls.sql: Displays plans for serial processing
  • utlxplp.sql: Shows plans including parallel execution columns

Advanced Configuration and Best Practices

Schema-Specific vs Global Setup

Organizations can choose between local schema-specific PLAN_TABLEs or shared global tables. The shared approach offers consistency and centralized management, while local tables provide isolation and customization opportunities.

Version Compatibility Considerations

Oracle Corporation recommends rebuilding PLAN_TABLE after database version upgrades. Column definitions may change between versions, potentially causing script failures or compatibility issues with tools like TKPROF.

Performance Monitoring Integration

PLAN_TABLE integrates seamlessly with Oracle's performance monitoring ecosystem. The PLUSTRACE role may be required for certain operations, created using the plustrce.sql script:

1-- Grant PLUSTRACE role for enhanced functionality 
2@$ORACLE_HOME/sqlplus/admin/plustrce.sql 
3GRANT plustrace TO username;

Query Optimization Strategies

Execution Plan Analysis

Effective execution plan analysis involves examining several key metrics:

  • Cost Estimates: Optimizer's resource usage predictions
  • Row Estimates: Expected number of rows processed
  • Access Methods: Table scans, index usage, join strategies
  • Parallel Operations: Multi-process execution indicators

Common Optimization Patterns

Successful query optimization typically follows these patterns:

  • Index Utilization: Ensuring appropriate index usage
  • Join Order Optimization: Minimizing intermediate result sets
  • Predicate Pushdown: Moving filter conditions closer to data sources
  • Parallel Processing: Leveraging multiple CPU cores for large operations

Integration with Modern Oracle Features

Oracle's execution plan functionality continues evolving with newer database versions. From Oracle 9i onward, DBMS_XPLAN became the preferred method for displaying execution plans4, offering enhanced formatting and additional analytical capabilities compared to traditional utility scripts.

The PLAN_TABLE infrastructure supports advanced Oracle features including:

  • Adaptive Query Optimization: Dynamic plan adjustments during execution
  • SQL Plan Management: Consistent plan enforcement across environments
  • Real-Time SQL Monitoring: Live execution tracking and analysis
  • Automatic Workload Repository: Historical performance data collection

Understanding and effectively utilizing Oracle's PLAN_TABLE and EXPLAIN PLAN functionality forms the foundation of successful database performance tuning. These tools provide essential insights into query execution strategies, enabling database administrators and developers to make informed optimization decisions that significantly impact application performance and user experience.

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