Tag Archives: Lock After Qualification

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June 4, 2026

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SQL Server 2025 Series : This New Locking Feature Changes Everything – Full Demo on Optimized Locking!

If you work with high-concurrency OLTP workloads, SQL Server 2025 Optimized Locking is one of the most practical improvements to understand. In this demo, we use two databases: one with optimized locking disabled and one with it enabled. Both databases are configured with Accelerated Database Recovery (ADR) and Read Committed Snapshot Isolation (RCSI), while only one database has OPTIMIZED_LOCKING = ON.

Why this feature matters

The real value of optimized locking is simple: it helps reduce lock footprint during write activity, which can lower blocking in busy systems. The attached demo is designed exactly for that comparison by creating two identical databases—Billing_OFF and Billing_ON—and toggling only the optimized locking setting between them.

Demo setup

Start by creating the two demo databases and enabling the required database options:

USE master;
GO
DROP DATABASE IF EXISTS Billing_OFF;
DROP DATABASE IF EXISTS Billing_ON;
GO
CREATE DATABASE Billing_OFF;
CREATE DATABASE Billing_ON;
GO
-- Both databases need ADR enabled
ALTER DATABASE Billing_OFF SET ACCELERATED_DATABASE_RECOVERY = ON;
ALTER DATABASE Billing_ON SET ACCELERATED_DATABASE_RECOVERY = ON;
GO
-- RCSI is needed for lock-after-qualification (LAQ) demo
ALTER DATABASE Billing_OFF SET READ_COMMITTED_SNAPSHOT ON WITH ROLLBACK IMMEDIATE;
ALTER DATABASE Billing_ON SET READ_COMMITTED_SNAPSHOT ON WITH ROLLBACK IMMEDIATE;
GO
-- Only one database gets optimized locking
ALTER DATABASE Billing_OFF SET OPTIMIZED_LOCKING = OFF;
ALTER DATABASE Billing_ON SET OPTIMIZED_LOCKING = ON;
GO
-- Verify settings
SELECT
    name,
    is_accelerated_database_recovery_on,
    is_read_committed_snapshot_on,
    is_optimized_locking_on
FROM sys.databases
WHERE name IN ('Billing_OFF', 'Billing_ON');
GO

Build the test table

Next, create the same table in both databases and open a transaction so you can inspect locks while the transaction is still active.

Setup for optimized locking OFF

USE Billing_OFF;
GO
DROP TABLE IF EXISTS dbo.InvoiceLedger;
GO
CREATE TABLE dbo.InvoiceLedger
(
    InvoiceId int NOT NULL,
    AmountDue decimal(10,2) NULL
);
GO
INSERT INTO dbo.InvoiceLedger (InvoiceId, AmountDue)
VALUES (1001, 1200.00),
       (1002, 850.00),
       (1003, 430.00);
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 50.00;
SELECT
    request_session_id,
    resource_type,
    request_mode,
    resource_description
FROM sys.dm_tran_locks
WHERE request_session_id = @@SPID
  AND resource_type IN ('PAGE', 'RID', 'KEY', 'XACT')
ORDER BY resource_type, request_mode;
-- Keep transaction open for observation
WAITFOR DELAY '00:00:20';
COMMIT TRAN;
GO

This script updates all rows and keeps the transaction open for 20 seconds so you can inspect the acquired locks in the Billing_OFF database.

Setup for optimized locking ON

USE Billing_ON;
GO
DROP TABLE IF EXISTS dbo.InvoiceLedger;
GO
CREATE TABLE dbo.InvoiceLedger
(
    InvoiceId int NOT NULL,
    AmountDue decimal(10,2) NULL
);
INSERT INTO dbo.InvoiceLedger (InvoiceId, AmountDue)
VALUES (1001, 1200.00),
       (1002, 850.00),
       (1003, 430.00);
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 50.00;
SELECT
    request_session_id,
    resource_type,
    request_mode,
    resource_description
FROM sys.dm_tran_locks
WHERE request_session_id = @@SPID
  AND resource_type IN ('PAGE', 'RID', 'KEY', 'XACT')
ORDER BY resource_type, request_mode;
WAITFOR DELAY '00:00:20';
COMMIT TRAN;
GO

This is the matching script for Billing_ON, allowing you to compare lock behavior when optimized locking is enabled.

Concurrency test

To demonstrate blocking behavior, open two sessions against each database.

Session 1 – hold an update open

Optimized locking OFF

USE Billing_OFF;
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 25.00
WHERE InvoiceId = 1001;
WAITFOR DELAY '00:00:20';
COMMIT TRAN;
GO

This session updates InvoiceId = 1001 and intentionally holds the transaction for 20 seconds.

Optimized locking ON

USE Billing_ON;
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 25.00
WHERE InvoiceId = 1001;
WAITFOR DELAY '00:00:20';
COMMIT TRAN;
GO

This is the same workload pattern, but executed in the database where optimized locking is enabled.

Session 2 – concurrent update

Optimized locking OFF

USE Billing_OFF;
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 25.00
WHERE InvoiceId = 1002;
COMMIT TRAN;
GO

Run this in a second session while Session 1 is still open.

Optimized locking ON

USE Billing_ON;
GO
BEGIN TRAN;
UPDATE dbo.InvoiceLedger
SET AmountDue = AmountDue + 25.00
WHERE InvoiceId = 1002;
COMMIT TRAN;
GO

Again, this is the same concurrent update, but without optimized locking.

Monitoring script

Use the following monitoring query to observe waits, request state, and lock information for both sessions while the demo is running:

-- Replace the session IDs below with the two session IDs used in your demo windows.
SELECT
    r.session_id,
    r.status,
    r.command,
    r.wait_type,
    r.wait_time,
    r.wait_resource,
    t.text
FROM sys.dm_exec_requests r
CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) t
WHERE r.session_id IN (62, 171);
GO
SELECT
    request_session_id,
    resource_type,
    request_mode,
    request_status,
    resource_description
FROM sys.dm_tran_locks
WHERE request_session_id IN (62, 171)
ORDER BY request_session_id, resource_type, request_mode;
GO

Expected takeaway

The demo is structured to show that the same update workload behaves differently depending on whether OPTIMIZED_LOCKING is OFF or ON. Because both environments are identically configured except for the optimized locking setting, any change in observed lock behavior is attributable to that feature.

Final thoughts

SQL Server 2025 Optimized Locking is not just a checkbox feature—it directly changes how you demonstrate concurrency, lock management, and blocking reduction to customers. If you want a clean live demo, the attached billing scripts are perfect because they isolate the feature clearly and make the before-vs-after comparison easy to explain.

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=-XQj5YtnuEY

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.