Optimizing Long-Running SQL Queries

In this blog post, we will explore various methods to find, analyze, and optimize long-running SQL queries in Oracle.

Indexing for Performance Improvement

Indexes can significantly improve query performance. To check for missing indexes, you can analyze execution plans using the following:

SELECT * FROM v$sql_plan WHERE sql_id = '<SQL_ID>';

If the execution plan shows full table scans where indexes could be useful, consider creating indexes:

CREATE INDEX idx_column_name ON table_name (column_name);

Optimizing Execution Plans

Use EXPLAIN PLAN to understand how Oracle executes queries:

EXPLAIN PLAN FOR SELECT * FROM employees WHERE department_id = 10;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

Review the execution plan and ensure the query is utilizing indexes efficiently.

Using Query Hints

SELECT /*+ INDEX(table_name index_name) */ column1, column2 FROM table_name WHERE column1 = 'value';

Partitioning Large Tables

Partitioning large tables can improve query performance by reducing the amount of data scanned:

CREATE TABLE sales_partitioned (

    sale_id NUMBER,

    sale_date DATE,

    amount NUMBER

)

PARTITION BY RANGE (sale_date) (

    PARTITION sales_2024 VALUES LESS THAN (TO_DATE('2025-01-01', 'YYYY-MM-DD')),

    PARTITION sales_2025 VALUES LESS THAN (TO_DATE('2026-01-01', 'YYYY-MM-DD'))

);