SA0026 : Local cursor variable not explicitly deallocated

Cursors should be deallocated before the end of a batch using the DEALLOCATE statement to avoiding resource leaks.

Description

Cursors provides a mechanism to iterate through the results of a query row by row. However, if not properly managed, cursors can lead to resource leaks by consuming memory and other resources if they are not closed and deallocated appropriately. This issue is particularly relevant in SQL Server where resource efficiency is crucial for performance.

Example of a cursor not being deallocated:

SQL
Copy
1DECLARE cursor_name CURSOR FOR
2SELECT column_name FROM TableName;
3
4OPEN cursor_name;
5FETCH NEXT FROM cursor_name;
6-- More cursor logic
7-- Missing DEALLOCATE statement

When a cursor is not explicitly deallocated, the resources it consumes remain allocated, which can degrade performance and lead to inefficient use of system resources. It’s crucial to avoid such scenarios by ensuring that every opened cursor is deallocated after use.

  • Resource consumption: Open cursors that are not deallocated continue to consume memory and CPU resources.

  • Potential for performance issues: Accumulation of undeallocated cursors can lead to degraded performance and increased load on the database server.

How to fix

To prevent resource leaks and ensure efficient use of system resources, explicitly deallocate the local cursor variable after it is no longer needed using the DEALLOCATE statement.

Follow these steps to address the issue:

  1. Declare the cursor using the DECLARE statement.

  2. Open the cursor with the OPEN statement to begin using it.

  3. Use FETCH statements to retrieve data and perform required operations.

  4. Close the cursor using the CLOSE statement once you have finished processing.

  5. Finally, deallocate the cursor using the DEALLOCATE statement to free up system resources.

Example of correctly handling a cursor:

SQL
Copy
1DECLARE cursor_name CURSOR FOR
2SELECT column_name FROM TableName;
3OPEN cursor_name;
4FETCH NEXT FROM cursor_name;
5-- More cursor logic
6CLOSE cursor_name;
7DEALLOCATE cursor_name;

Scope

The rule has a Batch scope and is applied only on the SQL script.

Parameters

Rule has no parameters.

Remarks

The rule does not need Analysis Context or SQL Connection.

Effort To Fix
2 minutes per issue.
Categories

Performance Rules, Bugs

Additional Information

There is no additional info for this rule.

Example Test SQL
SQL
Copy
 1DECLARE @MyVariable CURSOR
 2
 3DECLARE MyCursor CURSOR FOR
 4SELECT LastName FROM AdventureWorks.Person.Contact
 5
 6SET @MyVariable = MyCursor
 7
 8/* Use DECLARE @local_variable and SET */
 9DECLARE @MyVariable1 CURSOR
10
11SET @MyVariable1 = CURSOR SCROLL KEYSET FOR
12SELECT LastName FROM AdventureWorks.Person.Contact;
13DEALLOCATE MyCursor;
14
15DEALLOCATE @MyVariable1;
16
17-- Uncomment the line below in order to deallocate the cursor variable
18--DEALLOCATE @MyVariable;
Analysis Results
  Message Line Column
1 SA0026 : Local cursor reference ‘@MyVariable’ not explicitly deallocated. 1 8
See Also

Other Resources

Analysis Rules