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Database Transactions Concepts and Features

Database transactions are vital for maintaining the accuracy and reliability of the information in a database. A transaction is a single logical unit of work that accesses and possibly modifies the contents of a database. Transactions encapsulate a set of related changes to the database; either all the changes in a transaction are applied, or none of them are.

Here are some key concepts and features associated with database transactions:

  1. ACID Properties: This acronym represents the four key properties of a database transaction.

    • Atomicity: This property ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure, and all the previous operations are rolled back to their former state.

    • Consistency: This property ensures that the database properly changes states upon a successfully committed transaction.

    • Isolation: This property enables transactions to operate independently of and transparent to each other.

    • Durability: This property ensures that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors.

  2. Transaction States: A transaction can be in one of the following states - Active, Partially Committed, Committed, Failed, and Aborted.

  3. Commit and Rollback: The process of persisting the changes of a transaction to the database is known as committing the transaction. If a transaction is successful, it is committed. Rollback is the process of undoing the changes made by the current transaction and is used when a transaction fails.

  4. Concurrency Control: It is essential when multiple transactions are executed concurrently. Concurrency control ensures that correct results for concurrent operations are generated while getting those results as quickly as possible.

  5. Transaction Log: The transaction log is a critical component of any transactional system. It holds the history of actions executed by a transaction. In case of a system failure, the logs are used to recover the data.

  6. Nested Transactions: Nested transactions are transactions that contain one or more other transactions. The outcome depends on the outcome of the parent transactions and the nested ones.

  7. Distributed Transactions: A single transaction that involves multiple network hosts. These are complex to handle, especially considering the ACID properties.

Understanding these principles and features of database transactions is essential for anyone designing, developing, or maintaining a database system, as they ensure data integrity and consistency, even in the face of system failures or errors.

  1. Transaction isolation levels in databases:

    • Transaction isolation levels define the degree to which one transaction must be isolated from the effects of other concurrent transactions.
    SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
    
  2. Rollback and commit in database transactions:

    • Use ROLLBACK to undo changes made during a transaction and COMMIT to save the changes permanently.
    START TRANSACTION;
    -- SQL statements
    COMMIT;
    -- or
    ROLLBACK;
    
  3. Concurrency control in database transactions:

    • Implement concurrency control mechanisms to manage simultaneous access to data and prevent conflicts between transactions.
    START TRANSACTION ISOLATION LEVEL SERIALIZABLE;
    -- SQL statements
    COMMIT;
    -- or
    ROLLBACK;
    
  4. Transaction control statements in SQL:

    • SQL statements for controlling transactions include BEGIN TRANSACTION, COMMIT, ROLLBACK, and SAVEPOINT.
    START TRANSACTION;
    -- SQL statements
    SAVEPOINT savepoint_name;
    -- Additional SQL statements
    ROLLBACK TO SAVEPOINT savepoint_name;
    COMMIT;