Description

which cursor is faster in sql server ?

### Which Cursor is Faster in SQL Server?

SQL Server is a robust relational database management system used widely for enterprise applications. A key aspect of working with SQL Server is using cursors, which are database objects that help us manipulate data in a set-based manner. However, the choice of cursor type can significantly impact performance. Let’s explore which cursor is typically faster in SQL Server, based on common practices and user feedback.

#### Fast-Forward Cursor vs. Other Cursor Types

When discussing cursor performance in SQL Server, the Fast-Forward Cursor is particularly renowned for its speed. This is primarily because it is optimized for moving forward and cannot scroll backward, making it well-suited for single-use, read-only scenarios. Moreover, it is a FORWARD_ONLY and READ_ONLY combination cursor. According to a discussion on Stack Overflow and the experience shared online, Fast-Forward Cursors are usually the fastest among the types users typically choose for looping through data.

However, comparing cursors directly against set operations is often a lesson in contrasting performance expectations. While a while loop can be faster than a cursor in many cases, set operations (using SELECT, INSERT, UPDATE, and DELETE statements) are generally faster and should be preferred whenever possible. Set operations leverage the SQL Server engine’s optimized execution plan capabilities, which can process large datasets more efficiently than cursors, even the more performant Fast-Forward variety.

#### The Case Against Cursors

Cursors can pose a significant performance bottleneck, especially with large data sets or frequent database updates. Often, developers lean towards cursors due to a need for procedural logic or processing each row individually, but this comes at a cost. SQL transactions, parallel processing, and other tools may not function as expected with cursors because they are inherently iterative, converting what could be a set-based operation into a row-by-row process.

A significant downside to cursors is their performance when dealing with large datasets. As per an account from a senior DBA who detailed performance issues encountered, a cursor-based query that started quickly bogged down as it iterated through a large data set, illustrating the overhead cursors add to database processing.

#### Alternatives to Cursors

If a cursor is necessary for procedural reasons, carefully select the cursor type based on the requirements:
1. **Fast-Forward**: If you just need to traverse a result set without modifying it.
2. **Forward-Only, Read-Only**: If you absolutely need to traverse in a forward-only direction but may need to update or delete rows.

In scenarios where procedural logic is less critical, consider alternatives like Common Table Expressions (CTEs), JOINs, or the use of temporary tables to optimize for performance. Using indexes, minimizing logical reads, and ensuring efficient use of set-based operations can drastically improve performance over using cursors.

### Conclusion

While the Fast-Forward Cursor may be the fastest of the cursor types, it’s important to remember that the best performance is usually achieved by leveraging the power of set-based operations in SQL Server. Cursors, and especially those not optimized for forward-only, read-only operations, should be a tool of last resort. Understanding when to pick a cursor over a set-based operation can significantly boost your SQL Server performance. For those rare cases where a cursor is necessary, using a Fast-Forward Cursor with proper configuration can help optimize cursor-driven tasks.

For a detailed, hands-on analysis, a video from experts or advanced SQL Server performance optimization articles, such as those found on SQL Shack and other SQL Server communities, offer in-depth knowledge on tackling performance issues effectively.

Keep in mind, the best method to enhance SQL Server performance is often to replace cursor logic with set-based logic where possible.