Difference between a generated execution plan and an actual execution plan (4379314)

This article explains the difference between Estimated Execution Plans and Actual Execution Plans in SQL Server. Understanding these differences is essential for performance tuning and query optimization.

SQL Server provides two types of execution plans to help analyze how queries are processed:

1. Estimated Execution Plan

• Description: A plan generated by the SQL Server Query Optimizer based on current statistics and indexes, without executing the query.

• Purpose: To preview how SQL Server intends to execute the query.

• Contains:

  • Operator choices (e.g., index seeks, scans, joins)

  • Estimated row counts

  • Estimated CPU and I/O costs

• Does Not Contain:

  • Runtime statistics

  • Execution warnings

• Usage: Use when you want to analyze the plan without affecting data or incurring performance overhead.

2. Actual Execution Plan

• Description: A plan that includes both the optimizer’s choices and actual runtime statistics collected during query execution.

• Purpose: To review how the query was actually executed and assess performance.

• Contains:

  • All elements of the estimated plan

  • Actual number of rows processed per operation

  • Execution warnings (e.g., spills to tempdb)

  • Operator-level execution time and resource usage

• Usage: Use when troubleshooting slow queries, verifying optimizer assumptions, or fine-tuning performance.

Comparison Table