Creating and Using DB2 Materialized Views (Performance Improvement)

Materialized View is a view created in the database, but unlike ordinary views, it physically stores query results into a table and reads directly from this table on each request. This design can significantly improve query performance.

When to Use Materialized Views

Usage Scenarios

1. Frequent Operations: If your application requires frequent insert, delete, or update operations on data, you can use materialized views to reduce unnecessary data writes and reads.

2. Complex Queries: For some complex SQL queries, using a materialized view directly can improve execution speed.

1. Static Data: If your data is static and does not change, you do not need to use materialized views.

2. Real-time Updates: Using transactions and triggers may be more appropriate for implementing real-time updates.

Creation of Materialized Views

Syntax

CREATE MATERIALIZED VIEW mv_name
AS 
SELECT *
FROM table_name;
  • CREATE: Must be in uppercase.
  • MATERIALIZED VIEW: Indicates this is a materialized view.
  • mv_name: Is the name of the materialized view.
  • AS: Specifies the statement used to create the materialized view.
  • SELECT * FROM table_name; : Is the SQL statement for creating the materialized view.

Triggers

CREATE TRIGGER tg_name
AFTER INSERT OR UPDATE ON table_name
FOR EACH ROW
EXECUTE PROCEDURE trigger_function();
  • CREATE: Must be in uppercase.
  • TRIGGER : Indicates this is a trigger.
  • tg_name: Is the name of the trigger.
  • AFTER INSERT OR UPDATE ON table_name;: The condition under which the trigger fires.
  • FOR EACH ROW: Specifies that the trigger should fire on each row of data.
  • EXECUTE PROCEDURE trigger_function(); : Specifies the function to be executed.

Reverse Triggers

CREATE TRIGGER tg_name
BEFORE INSERT OR UPDATE ON table_name
FOR EACH ROW
EXECUTE PROCEDURE trigger_function();
  • This trigger fires only when data is inserted or updated.

Usage and Management of Materialized Views

Determining Whether a Materialized View Is Needed

1. Data that changes frequently needs to be accessed via materialized view.

2. Real-time updates or triggers need to be implemented using materialized views.

Maintenance of Materialized Views

  • Delete the materialized view through the DROP MATERIALIZED VIEW command.
  • Modify the structure of the materialized view through the ALTER MATERIALIZED VIEW command.
  • Analyze the materialized view through the ANALYZE MATERIALIZED VIEW command.

Performance Optimization

1. Reduce Data Write Volume: Only update data that needs to change, reducing unnecessary data writes.

2. Reduce Data Read Volume: Extract only the required data from the materialized view.

3. Improve Initial Speed of Materialized View: Use optional parameters (such as REPLAIN) in CREATE MATERIALIZED VIEW to improve the initial speed of the materialized view.

Optimizing Triggers

  • Reduce Trigger Frequency: Use BEFORE INSERT OR UPDATE triggers to reduce trigger frequency.
  • Reduce Data Write Volume: Only update data that needs to change, reducing unnecessary data writes.