Understanding Locks in SQL Server – A Complete Guide

When we talk about balancing performance while maintaining data accuracy, it becomes a challenging task, even for database administrators. This is where locks in SQL Server come in handy. But what are these locks? Not all of us are aware of this concept, and further face challenges when any issue related to SQL Server lock is encountered. 

With the help of this technical write-up, we will be learning more thoroughly about what these locks are and how we can resolve issues created by them. 

What Are Locks in SQL Server & How Do They Work?

SQL Server locks can be simply defined as a temporary hold that prevents a user from accessing data or a record that is already being used by another process or user. To simplify the definition, let’s take a look at how this works. When a transaction uses a record or data, the lock in SQL Server holds it so that any other transaction does not further use it. Once the transaction is completed, the lock is then released from that specific record. 

The major benefit of locks in SQL Server is that they help maintain the ACID properties of a transaction. ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties collectively help the transactions in SQL Server to be processed efficiently, while maintaining data consistency and precision. Here are a few common types of locks usually worked with in SQL Server:

• Shared Locks
• Exclusive Locks
• Update Locks
• Intent Locks
• Schema Locks
• Bulk Update Locks

So, by this, we now understand how important locks are in SQL Server. Moving on to how these locks work, let’s take a look at the steps. 

Step-by-Step Working of SQL Server Locks Explained

We will now take a look at the working process of locks and understand how they help with accurate data processing. 

1. The transaction is initiated by the user in the SQL Server Database.
2. A lock request is then sent to the lock manager for a specific record or data.
3. Next, the lock manager checks and verifies lock compatibility over the resource. If they are compatible, then the transaction can proceed. 
4. After the compatibility check, the lock is granted for the required resource. 
5. Next, after the locks in SQL Server are granted, the transaction is executed. 
6. Once all these steps are completed, the locks remain intact till the transaction is either completed or failed. 
7. After the completion, the locks are then released. Once the locks completely release the resources, other waiting transactions can then proceed to access the specified resource. 

These are the steps on how locking in SQL Server helps with holding a resource till a transaction is completed. So far, we have understood the importance of locks in SQL Server. But are these locks completely safe? The answer is No. There are various scenarios in which users have encountered several challenges due to these locks. Let’s take a look at them and find the best solutions to resolve them efficiently. 

Challenges Encountered Due to SQL Server Locks

Here we have mentioned a few of the common challenges encountered by users while they use lock in SQL Server. Let’s understand them thoroughly and further find the best approach of resolving them.

1. The most common issue encountered by users is blocking in transactions. When a resource is locked that is required by various other transactions, they are supposed to wait for the first transaction to be finished. This leads to blocking in SQL Server.
2. The next issue encountered in the database is a SQL Server deadlock issue. When two transactions require two different resources acquired by each of the two transactions, it creates a circular loop. This further results in freezing the transactions till one of the resources is released. 
3. Another issue encountered is the long-running queries in SQL Server. With the resources and records acquired with locks, the transactions take longer to complete, further delaying the entire process. 

With these issues already in the server, if the user or database administrator encounters a server crash while the transactions are on hold or locked, it will leave the transactions midway and can further result in database corruption. With a corrupted SQL Server database, the required processes cannot be completed, which further leads to the risk of data loss in the database. In such situations, it is better to use a professional and reliable solution. Let’s take a look at how an advanced tool can help with this. 

Fix Database Corruption Caused Due to Locks in SQL Server Professionally

Here, to resolve this issue and recover the affected database file (.mdf file), we will now use the SysTools SQL Recovery Tool. This is an advanced and expert-recommended solution that allows database administrators to recover the damaged databases and preserve the data integrity throughout.

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Let’s take a look at the steps on how we can use the tool to repair database damage due to SQL Server locks.

1. Install and run the suggested software. Click on Open to add MDF files.
2. The tool will offer two scan modes: Quick Scan and Advance Scan. Choose one.
3. After the scan, preview the recovered data. Then, click on the export button to restore the data from SQL database.
4. Now, in the Export Window, choose the export option, and add the authentication details.
5. Select the database objects to be restored and then click on the export button to resolve issues caused due to locks in SQL.

Following these steps, a user can effectively secure their data after a server crash or locking issue. 

Conclusion

With the help of this write-up, we have learned thoroughly about lock in SQL Server and further its functionality. Along with the work, we have also mentioned how these locks can create challenges for the users and further suggested the best way to resolve the issue seamlessly.