Parallelism tuning has always been one of the most challenging aspects of SQL Server performance optimization. DBAs often spend hours fine-tuning MAXDOP settings, trying to strike the perfect balance between performance and resource consumption.

With SQL Server 2025, this challenge is significantly reduced thanks to Degree of Parallelism (DOP) Feedback—a powerful Intelligent Query Processing feature that automatically optimizes parallel query execution.

In this blog, we will walk through:

• What DOP Feedback is
• How to track it using Extended Events
• A real-time demo with multiple scenarios
• How to validate whether DOP Feedback is working on your server

What is DOP Feedback?

DOP Feedback enables SQL Server to self-adjust the degree of parallelism for repeated queries. Instead of relying on static MAXDOP settings, SQL Server analyzes runtime performance (CPU usage, execution time, waits) and dynamically tunes DOP for subsequent executions.

This helps:

• Reduce excessive CPU usage
• Improve query performance
• Eliminate manual tuning effort

Tracking DOP Feedback using Extended Events

To understand how SQL Server applies DOP Feedback, we can capture internal engine decisions using Extended Events.

Setup DOP Feedback Tracking

IF EXISTS (SELECT 1 FROM sys.server_event_sessions WHERE name = 'DOPFeedbackWatch')
    DROP EVENT SESSION DOPFeedbackWatch ON SERVER;
GO
CREATE EVENT SESSION DOPFeedbackWatch ON SERVER
ADD EVENT sqlserver.dop_feedback_eligible_query(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_provided(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_validation(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_stabilized(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_reverted(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_analysis_stopped(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash)),
ADD EVENT sqlserver.dop_feedback_reassessment_failed(
    ACTION(sqlserver.sql_text, sqlserver.plan_handle, sqlserver.query_hash))
ADD TARGET package0.ring_buffer;
GO
ALTER EVENT SESSION DOPFeedbackWatch ON SERVER STATE = START;
GO

What this captures

This session helps us track:

• When a query becomes eligible for DOP Feedback
• When SQL Server adjusts DOP
• Whether feedback is validated or reverted
• When the system stabilizes on an optimal DOP

This gives real-time visibility into the self-tuning engine behavior.

DOP Feedback Demo (Step-by-Step)

Let’s simulate workloads to observe DOP Feedback in action.

Scenario 1: High-Volume Parallel Query (Feedback Adjusted)

CREATE DATABASE jbdb
GO
USE JBDB
GO
--Create table and load table
CREATE TABLE [dbo].[Table1]([Col1] [int] IDENTITY(1,1) ON [PRIMARY]
GO
set nocount on
insert into Table1 (Col2, Col3, Col4, Col5) values (1, REPLICATE ('a',4000), 10, 100)
go 999
insert into Table1 (Col2, Col3, Col4, Col5) values (2, REPLICATE ('z',4000), 11, 100)
go 99999
insert into Table1 (Col2, Col3, Col4, Col5) values (3, REPLICATE ('f',4000), 12, 100)
go 8965
insert into Table1 (Col2, Col3, Col4, Col5) values (4, REPLICATE ('g',4000), 13, 100)
go 7844
insert into Table1 (Col2, Col3, Col4, Col5) values (5, REPLICATE ('u',4000), 14, 100)
go 4567
insert into Table1 (Col2, Col3, Col4, Col5) values (2, REPLICATE ('z',4000), 11, 100)
go 751049
-- Stored Procedure to query the table
CREATE OR ALTER PROCEDURE [dbo].[usp_GetDetails] @Col2 int
AS
BEGIN
SELECT top (50000)
    [Col1], 
    [Col2], 
    [Col3], 
    [Col4], 
    [Col5]
FROM dbo.Table1
WHERE [Col2] = @Col2
ORDER BY [Col3];
END
--EXECUTE the stored procedure
EXEC [dbo].[usp_GetDetails] @Col2 = 2
--OSTRESS
C:\Program Files\Microsoft Corporation\RMLUtils>ostress -S"VIJANAK\IN2025" -E -Q"EXEC usp_GetDetails @Col2 = 2;" -n1 -r100 -q -dJBDB

In this scenario:

• Query executes repeatedly under load
• SQL Server identifies inefficiencies in parallelism
• DOP is adjusted for better performance

Scenario 2: Skewed Parallelism (Feedback Evaluation)

use JBBlog
[dbo].[usp_SkewedParallelReport]
ostress -S"VIJANAK\IN2025" -E -Q"EXEC usp_SkewedParallelReport;" -n1 -r100 -q -dJBBlog

Here:

• SQL Server evaluates skewed workloads
• Determines whether reducing DOP improves efficiency
• May validate or reject feedback

Monitoring Live Workload

To see what is actively running:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
  -- What SQL Statements Are Currently Running?
  SELECT [Spid] = session_Id
, ecid
, [Database] = DB_NAME(sp.dbid)
, [User] = nt_username
, [Status] = er.status
, [Wait] = wait_type
, [Individual Query] = SUBSTRING (qt.text,
      er.statement_start_offset/2,
(CASE WHEN er.statement_end_offset = -1
    THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2
ELSE er.statement_end_offset END -
                er.statement_start_offset)/2)
,[Parent Query] = qt.text
, Program = program_name
, Hostname
, nt_domain
, start_time
  FROM sys.dm_exec_requests er
  INNER JOIN sys.sysprocesses sp ON er.session_id = sp.spid
  CROSS APPLY sys.dm_exec_sql_text(er.sql_handle)as qt
  where session_Id NOT IN (@@SPID)   -- Ignore this current statement.
  ORDER BY 1, 2
  go

This helps you:

• Identify active queries
• Validate parallel workloads
• Correlate with Extended Event output

Key Observations from the Demo

From the above scenarios, you will typically notice:

1. DOP Feedback Applied Successfully
   • SQL Server reduces or adjusts DOP
   • Performance improves over repeated executions
2. Optimal DOP Identified
   • No change needed
   • System confirms current DOP is efficient
3. Query Not Eligible
   • Some queries are excluded
   • Depends on execution pattern and workload

Why This Matters

DOP Feedback fundamentally changes how DBAs approach tuning:

Watch the Full Demo

I’ve recorded a complete walkthrough of this setup on my YouTube channel JBSWiki. If you’re a visual learner, go check it out!

👉 Watch here: https://www.youtube.com/watch?v=nVMeQeiUKTA

Final Thoughts

With SQL Server 2025, the database engine becomes smarter and more autonomous.

DOP Feedback:

• Eliminates guesswork
• Improves performance stability
• Reduces CPU contention
• Adapts dynamically to workload changes

For DBAs and performance engineers, this means less time tuning and more time delivering value.

If you are testing SQL Server 2025 in your environment, I highly recommend running this demo and observing the Extended Events output — it gives incredible insight into how the engine learns and adapts in real time.

Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.