What Causes SQL Deadlock When Calling REST Procedure?

What is an SQL Deadlock?

An SQL deadlock is a situation that occurs when there are two different transactions waiting for completion from each other. This situation could continue without intervention, resulting in delayed responses or even failures in transactions.

In REST procedures, an SQL deadlock takes place when an SQL query is provided and two similar REST calls are made to the same query. The second call would have to wait for the first one to complete. This situation would either lead to a delayed response or a failure.

A Deadlock Example

A good example of a deadlock can occur when there are two queries that need to gain access to different tables with each one of them waiting for the other one to finish. Let us assume that we have two queries, qA, and qB. We also have two tables, t1 and t2. qA then accesses and locks t1 while qB does the same on t2.

With such a setup, there is nothing wrong happening. However, qA goes ahead and requests access to t2. Here, there exists a block. qA will be forced to wait for qB to remove its lock on t2 for it to gain access and process. This is where a deadlock occurs.

Ways of Minimizing Deadlocks

There are many ways of minimizing deadlocks. When building APIs, developers are supposed to make sure that they implement the right API management strategies and have the right API gateways within API management. These two concepts are very vital when improving the performance of REST procedures, which includes identifying the chances of deadlocks taking place.

Some developers and database administrators think that running the affected transactions, again and again, is the only thing they can do when handling deadlocks. However, there are a number of other things they can do to minimize deadlocks to avoid delays in their applications and reduce performance problems. They include;

Lowering the Transaction Level of Databases

Even though you might get problems with concurrency when you lower the transaction levels of your database, you will also improve the performance of the database. The concurrency problems might affect the uncommitted levels that are the lowest read but will not affect the highest serializable levels.

However, when considering improving the performance of your database with this technique, you need to do it carefully and implement it depending on different cases. Databases with a lot of static data being read by transactions are safe when lowering the database’s transaction level. On the other hand, developers need to be careful with data that can be modified in a database as it might lead to concurrency problems.

Improving the Performance of their Databases

A situation where there is a transaction taking more time to run than usual increases the chances of having a deadlock. The more time a query takes when running, then the more time it holds the resources that it is using. Developers can employ a number of tricks such as the following to improve the performance of their databases and reduce the chances of deadlocks taking place;

• Avoiding the use of cursors.
• Ensuring the smallest data types are implemented for table columns.
• Employing normalized data when writing and denormalized data when reading.
• Implementing covering, clustered, and non-clustered indexes.
• Ensuring query predicates are narrowed and not retrieving all columns.

Using the Same Order when Accessing Objects

One of the most common ways of reducing the chances of an SQL deadlock taking place is by making sure that objects are accessed in the same order. Imagine a situation where two REST procedures are accessing a certain table in a database. The table has 20 rows. The two procedures need to access all the rows, and in order.

The first procedure starts with row one while the other procedure starts with row twenty. These two procedures will meet at a certain row, and one of them will have to wait for the other one to finish before it gains access. This will lead to a deadlock. However, if they both used the same order when accessing the table, then the chances of a deadlock occurring would be minimized.

Using Tools to Identify Deadlock Issues

There are different tools that developers and database administrators can use to identify any issues that might exist and lead to deadlocks. One of the most common tools one can use is the SentryOne SQL Deadlock Tool. This tool comes with an amazing feature called Optimize Layout that gets rid of most of the repetitive nodes that make it difficult for one to troubleshoot deadlock issues.

These types of tools are very important when it comes to detecting and capturing deadlocks. They offer dashboards through which developers and database administrators can get a complete view of any chances of deadlocks occurring, or any that exist. Through the dashboards, they can see the resources and processes causing the deadlocks and perform an analysis of any statements that might be leading to deadlocks. This way, they are able to troubleshoot and get rid of deadlocks.

In conclusion, every developer is supposed to make sure that their applications meet both their expectations and those of their customers. A customer is likely to look for a competitor application if they experience delays due to issues caused by things like deadlocks. It is, therefore, important for them to have a database monitoring plan to improve the performance of the databases and use the right tools to identify any chances of deadlocks taking place.