Cursor Performance FAQS

1. What is cursor performance in Oracle?

Cursor performance refers to how efficiently Oracle fetches and processes rows from a SQL query using cursors.

Inefficient cursors can cause:

• Slow execution for large datasets
• High CPU and memory usage
• Excessive network round-trips in multi-tier applications

2. Which cursor types impact performance the most?

Cursor Type	Performance Notes
Implicit Cursor	Fast for single-row SELECT INTO and DML statements; automatically managed
Explicit Cursor	Slower if fetching row-by-row; requires manual OPEN/FETCH/CLOSE
Cursor FOR Loop	Faster than explicit cursor loops; automatically handles resources
REF CURSOR	Useful for returning result sets; performance depends on query and fetch logic

3. Why is row-by-row fetching slow?

• Each FETCH in explicit cursors requires a context switch between SQL engine and PL/SQL engine
• For large datasets, this overhead accumulates and slows execution

Solution: Use Cursor FOR Loops, BULK COLLECT, and FORALL

4. How does BULK COLLECT improve cursor performance?

• Fetches multiple rows at once into a PL/SQL collection
• Reduces SQL ↔ PL/SQL context switches

DECLARE

   TYPE emp_tab IS TABLE OF employees.employee_id%TYPE;

   v_emp_ids emp_tab;

BEGIN

   SELECT employee_id BULK COLLECT INTO v_emp_ids

   FROM employees

   WHERE department_id = 10;

END;

Best for large result sets

5. How does FORALL improve performance for DML?

• Executes DML statements in bulk on collections
• Minimizes context switches and reduces CPU usage

FORALL i IN v_emp_ids.FIRST .. v_emp_ids.LAST

   UPDATE employees

   SET salary = salary * 1.1

   WHERE employee_id = v_emp_ids(i);

6. How can I reduce cursor overhead?

1.    Fetch only required columns – avoid SELECT *

2.    Fetch only required rows using WHERE clauses

3.    Use bind variables – improves parsing and cursor reuse

4.    Avoid opening cursors inside loops – open once, fetch many

5.    Use parameterized cursors to reuse cursor structure with different values

7. How do bind variables improve cursor performance?

• Allow Oracle to reuse the same cursor for different input values
• Reduces hard parsing and improves memory usage

SELECT employee_id FROM employees WHERE department_id = :dept_id;

8. How can REF CURSORs affect performance?

• Returning large result sets via REF CURSOR can be slow if:
• Fetching rows one by one
• Cursor is not closed properly
• Using BULK COLLECT with REF CURSOR improves performance

9. How can I monitor cursor performance?

• Check open cursors:

SELECT user_name, COUNT(*)

FROM v$open_cursor

GROUP BY user_name;

• Track SQL execution statistics with V$SQL and V$SQLAREA
• Look for frequent hard parses, high CPU usage, or long fetch times

10. Common mistakes that degrade cursor performance

• Fetching all columns unnecessarily
• Row-by-row processing instead of BULK COLLECT
• Opening and closing cursors inside loops
• Not using bind variables
• Not closing explicit or REF CURSORs

11. Quick performance comparison

Approach	Performance
Row-by-row FETCH (explicit)	Slow
Cursor FOR Loop	Faster, auto-close
BULK COLLECT + FORALL	Fastest for large datasets
Implicit cursor DML	Fast for single-row operations

12. Best practices summary

• Use implicit cursors for single-row queries and DML
• Use Cursor FOR Loops for multi-row processing
• Use BULK COLLECT and FORALL for large datasets
• Minimize rows and columns fetched
• Reuse cursors with bind variables
• Always close explicit and REF CURSORs
• Avoid opening cursors inside loops
• Monitor open cursors in production