LCK_M_X Wait Type: A Deep Demystifying

LCK_M_X wait type is very important & need to manage properly. The performance of SQL Servers, which are the foundation of data-driven applications, must be optimized. This paper solves the puzzles around LCK_M_X wait types, a crucial component of SQL Server administration. You’ll acquire a thorough grasp of LCK_M_X waits, their historical importance, pros, and downsides, causes, preventive methods, and real-world examples, all of which are intended to help you improve the productivity of your SQL Server.


This wait type is known as LCK_M_X, or “Lock Manager Exclusive,” commonly arises in SQL Server setups. These waits represent a process’s request for exclusive access to a resource that is presently being held hostage by another process, such as a table or a page. It’s essential to comprehend LCK_M_X waits if you want to keep your SQL Server system’s integrity and performance intact.

A Glimpse into History

The development of SQL Server is linked with the history of LCK_M_X delay types. The necessity for effective resource locking and isolation increased along with the demand for strong data management solutions. To control exclusive access to resources, guarantee data consistency, and avoid conflicts, LCK_M_X waits were implemented.

You may like this article: Tips to minimise TempDB utilisation in Microsoft SQL Server

Advantages and Disadvantages

In SQL Server, the “LCK_M_X” (Lock Manager Exclusive) wait type is connected to exclusive locks and has a unique combination of benefits and drawbacks:

Advantages of LCK_M_X wait type:

Advantages of the LCK_M_X wait types in SQL Server are given below:

Modification of data:

When a transaction seeks an exclusive lock on a resource to carry out data modification operations like inserts, updates, or deletes, LCK_M_X wait types are generated. To avoid data conflicts, exclusive locks make sure that only one transaction at a time can alter the resource.

Data Consistency

By prohibiting other transactions from viewing or changing the data while it is being altered, exclusive locks preserve data consistency. By doing this, it is made sure that the data maintains its consistency throughout the alteration.

Data Integrity

LCK_M_X wait types support data integrity by preventing concurrent access to the resource by other transactions. This is essential to avoid scenarios in which many transactions could accidentally overwrite each other’s modifications.

You may also like this article: PAGEIOLATCH_EX: A Deep Dive

Disadvantages of LCK_M_X wait type:

Disadvantages of the LCK_M_X wait types in SQL Server are given below:


The main drawback of LCK_M_X wait types is their propensity to cause blocking. When a transaction has an exclusive lock on a resource, all subsequent transactions that need a lock of any kind—shared, updated, or exclusive—on the same resource will be halted until the exclusive lock is released. Performance bottlenecks and query execution delays may follow from this.


A deadlock occurs when many transactions are each holding their own while waiting for the other to release exclusive locks. Exclusive locks may be a factor in this situation. Deadlocks can prevent the SQL Server from operating normally, hence approaches for identifying and resolving deadlocks are necessary.

Reduced Concurrency

Despite being necessary to maintain data integrity, LCK_M_X locks can reduce concurrency by blocking other transactions from accessing the same resource. In high-transaction settings, excessive use of exclusive locks can lead to conflicts and slower query execution.

Resource Contention

Competition for exclusive locks may occur when numerous transactions need to make modifications to the same resource at once. The performance of the query execution might be hampered by this conflict.

LCK_M_X with Wait Time

Why Do LCK_M_X Wait Types Occur?

The principal cause of the “LCK_M_X” (Lock Manager Exclusive) delay type in SQL Server is as follows:

Exclusive Lock Request

When a transaction in SQL Server seeks an exclusive lock on a resource (such as a row, a page, or a table) to carry out a data modification operation, such as an insert, update, or deletion, LCK_M_X waits to happen.

Resource Exclusivity

To make sure that only one transaction may alter a resource at once, exclusive locks are utilized. Until the exclusive lock is released, a transaction that has an exclusive lock on a resource prevents other transactions from using that resource.

Data Consistency and Integrity

The basic goal of LCK_M_X locks is to protect the consistency and integrity of data. Exclusive locks avoid data conflicts by prohibiting several transactions from altering the same data at the same time. This keeps the data consistent.


When a single transaction has an exclusive lock on a resource, any subsequent transactions that try to obtain a lock of any kind—shared, updated, or exclusive—on the same resource will be prevented until the exclusive lock is released. This blocking is required to stop concurrent updates that can corrupt data.

Deadlock Prevention

Exclusive locks contribute to the prevention of deadlocks. They lessen the possibility of transactions becoming stuck while waiting for one another to release locks by assuring that only one transaction may alter a resource at once.

How to Avoid LCK_M_X Wait Type

Consider using the following tactics to prevent LCK_M_X (Lock Manager Exclusive) wait types in SQL Servers and enhance performance:

Optimize Queries

Queries should be optimized since doing so can lessen the possibility of LCK_M_X delays. To reduce the requirement for exclusive locks, make sure your queries are effective, make use of proper indexing, and only get the information that is required.

Transaction Isolation Levels

Select the right transaction isolation level for your queries from the list of available levels. When it offers the required data consistency, choose a lesser isolation level, such as READ COMMITTED, since it can lessen contention for exclusive locks.

Avoid Unnecessary Locks

Consider the granularity of your locks. Instead of locking whole tables or substantial amounts of data, lock just the individual rows or resources that need to be updated.

Reduce Transaction Time

Keep transactions as brief as you can. The possibility that many processes will simultaneously require exclusive access to the same data reduces as transaction times are lengthened.

Resource Allocation

Make sure your SQL Server has enough RAM and CPU power to execute many write operations concurrently without experiencing any noticeable delays. Contention about exclusive locks may be managed with adequate resource allocation.

Batch Operations

Utilise batch processes while inserting, updating, or deleting data in bulk. You may shorten the time that exclusive locks are held in place and lessen conflict by splitting up big activities into smaller batches.


Implement data partitioning techniques to split data among several file groups or discs. As a result, there will be less competition for exclusive access to particular data segments and I/O activities will be distributed.

Deadlock Detection

Implement tools for deadlock detection and resolution to swiftly end deadlock situations when they arise, lessening the effects of lock contention.

Snapshot Isolation

If your application can benefit from snapshot isolation, take into account utilizing it. By giving each transaction a consistent copy of the data, snapshot isolation enables higher levels of concurrency.

Lock Hints

Use lock hints sparingly to manage locking behavior in certain queries. When data consistency is not crucial, you can use the (NOLOCK) indication, for instance, to permit dirty reads.


For developers and administrators of SQL Server looking for the best performance, mastering LCK_M_X wait types is crucial. You can maximize the potential of your SQL Server system by learning about its origins, benefits, drawbacks, causes, and mitigation techniques. Remember that reducing LCK_M_X waits and guaranteeing efficient database operations need a mix of query optimization, good transaction design, and correct indexing.


Q: What does LCK_M_X stand for?
The acronym LCK_M_X stands for “Lock Manager Exclusive.”

Q: Do SQL Servers frequently experience LCK_M_X waits?
Yes, they do occur often in settings with several concurrent users and intricate transactions.

Q: Can data corruption result from LCK_M_X waits?
No, they allow for exclusive access in order to prevent data corruption.

Q: Do read-only queries suffer from LCK_M_X waits?
No, in most cases, because read-only queries don’t ask for exclusive locks.

Q: How can I tell whether my SQL Server has any LCK_M_X waits?
Track delay statistics using SQL Server’s performance monitoring tools.

Q: Is LCK_M_X delays only remedy query optimization?
While optimization is helpful, good indexing and transaction design are equally important.

Q: Can I give processes priority while LCK_M_X waits?
Although there are ways in SQL Server to do so, cautious planning is preferred.

Q: Can LCK_M_X wait to be eliminated entirely?
In highly concurrent environments, complete elimination may be challenging, but they can be significantly reduced.

Q: What’s the difference between LCK_M_X and LCK_M_S waits?
LCK_M_X wait represents exclusive access requests, while LCK_M_S wait signifies shared access requests.

Q: Should I be concerned about occasional LCK_M_X waits?
Occasional waits are normal, but consistently high waits may require further investigation.

Extended Events in SQL Server: A Deep Dive

SQL Server Database Mail

Query Store: A Powerful Tool

Understand Deadlocks in SQL Server


Leave a Comment