Database Transactions Overview

Study Notes

Database Transactions

A transaction is defined by the ANSI SQL standard as "a sequence of operations performed within a single user task". It ensures each operation must either complete successfully or be rolled back if it fails. A transaction applies to multiple related data modifications, which can occur over time and involve several users. In databases, transactions ensure that these changes appear atomic and consistent despite interruptions.

Let's discuss various aspects of database transactions:

ACID Properties

The acronym ACID refers to four properties that guarantee the reliability of database transactions: Atomicity, Consistency, Isolation, and Durability. These properties ensure data integrity by ensuring each transaction is reliable, consistent, and recoverable. Let's briefly discuss each property:

Atomicity

The atomicity property ensures that a transaction either completes in its entirety or is rolled back, so that the database remains consistent.

Consistency

The consistency property ensures that the database is in a valid state before and after the transaction.

Isolation

The isolation property ensures that the transaction is executed independently, without interference from other transactions.

Durability

The durability property ensures any changes in the database persist after a transaction is completed.

Isolation Levels

Isolation levels are specific rules that determine the level of isolation between transactions in a database system. There are four commonly used isolation levels:

Serializable

The serializable isolation level ensures that no two transactions can execute concurrently if there is any possibility of a conflict between them.

Repeatable Read

In repeatable read isolation, a transaction cannot see any changes made by another transaction that was started after the current transaction began.

Read Uncommitted

In read uncommitted isolation, a transaction can see the changes made by another transaction, even before the second transaction has been committed.

Read Committed

In read committed isolation, a transaction cannot see any changes made by another transaction until the second transaction has been committed.

Commit and Rollback

Commit and rollback are two operations in the context of database transactions.

Commit

The commit operation is used to confirm that all the operations within a transaction have been completed effectively and the transaction is ready to be completed.

Rollback

The rollback operation is used to undo all the operations within a transaction, effectively reverting the database to its state before the transaction was started.

Concurrency Control

Concurrency control is a set of techniques used to manage the simultaneous execution of transactions in a database system. These techniques ensure that transactions execute without interference and maintain the ACID properties of the database. There are three main types of concurrency control techniques:

Locking

Locking involves locking specific rows or tables to prevent other transactions from modifying them until the locked transaction completes.

Timestamping

Timestamping assigns time stamps to transactions based on their arrival order in the system, with older transactions having priority over newer ones.

Optimistic Concurrency Control

Optimistic concurrency control assumes that conflicts between transactions will not occur frequently in a high-concurrency environment.

Database Recovery

Database recovery is the process of restoring a damaged database back to its previous state. This process is essential in case of software bugs, power failures, or hardware failures. It involves two stages: crash recovery and media recovery. Crash recovery deals with restoring information after a failure during execution, while media recovery handles data loss due to physical damage or corruption.

In conclusion, understanding the various aspects of database transactions, including ACID properties, isolation levels, commit and rollback operations, concurrency control techniques, and database recovery methods, is crucial for maximizing data integrity and consistency within any database system.

Description

Explore the key aspects of database transactions, including ACID properties, isolation levels, commit and rollback operations, concurrency control techniques, and database recovery methods. Understanding these concepts is crucial for maintaining data integrity and consistency in database systems.