Oracle Database: Statements Requiring Commit to Avoid Locks

In Oracle Database, transaction management is crucial for maintaining data integrity and concurrency control. Certain operations necessitate explicit commit or rollback to avoid locks that can hinder further actions on tables.

Definition of DML Commands

Data Manipulation Language (DML) statements are used to manage data within schema objects. They include commands that modify data, and typically require a commit to make changes permanent.

List of DML Statements Requiring Commit

Based on Oracle documentation and best practices, the following DML statements need to be committed:

• INSERT - Inserts new rows into a table. For example: INSERT INTO employees (id, name) VALUES (1, 'John Doe');
• UPDATE - Updates existing rows in a table. Example: UPDATE employees SET name = 'Jane Doe' WHERE id = 1;
• DELETE - Deletes rows from a table, but space remains. Example: DELETE FROM employees WHERE id = 1;
• MERGE - Performs an UPSERT operation (insert or update). Example: MERGE INTO employees e USING (SELECT 1 AS id, 'New Name' AS name FROM dual) s ON (e.id = s.id) WHEN MATCHED THEN UPDATE SET e.name = s.name WHEN NOT MATCHED THEN INSERT (id, name) VALUES (s.id, s.name);
• CALL - Calls a PL/SQL or Java subprogram. Example: CALL my_procedure();
• EXPLAIN PLAN - Explains the access path to data. Example: EXPLAIN PLAN FOR SELECT * FROM employees;
• LOCK TABLE - Controls concurrency by locking tables. Example: LOCK TABLE employees IN EXCLUSIVE MODE;

These statements require a commit to finalize the changes and release locks.

Why Commit is Necessary to Avoid Locks

When DML statements are executed without a commit, the changes are held in a transaction. This can lead to locks on the affected rows or tables, preventing other sessions from accessing or modifying the data until the transaction is completed with a commit or rollback. Committing releases the locks and makes the changes permanent.

Code Example with Commit

Here's a simple example illustrating the use of commit:

-- Start a transaction
INSERT INTO employees (id, name) VALUES (2, 'Alice');
UPDATE employees SET name = 'Bob' WHERE id = 1;
-- Commit the changes
COMMIT;

Without the COMMIT, the changes are not persisted, and locks may remain.

In summary, understanding which statements require commit is essential for effective Oracle database management to avoid concurrency issues.