Transation in data base management system.pptx
- 1. Transaction By : Ayush Agrawal Data Base management system
- 2. 2 Introduction to TRANSACTION Transactions refer to a set of operations that are used for performing a set of logical work. Usually, a transaction means the data present in the DB has changed. Protecting the user data from system failures is one of the primary uses of DBMS.
- 3. 3 A user can make different types of requests to access and modify the contents of a database. So, we have different types of operations relating to a transaction. Operations of transaction • i) Read(X) A read operation is used to read the value of X from the database and store it in a buffer in the main memory for further actions such as displaying that value. • ii) Write(X) A write operation is used to write the value to the database from the buffer in the main memory. For a write operation to be performed, first a read operation is performed to bring its value in buffer, and then some changes are made to it. • iii) Commit Due to some failure of power, hardware, or software, etc., a transaction might get interrupted before all its operations are completed. To ensure that further operations of any other transaction are performed only after work of the current transaction is done, a commit operation is performed to the changes made by a transaction permanently to the database. • iv) Rollback This operation is performed to bring the database to the last saved state when any transaction is interrupted in between due to any power, hardware, or software failure.
- 4. 4 Transaction Schedules When multiple transaction requests are made at the same time, we need to decide their order of execution. Thus, a transaction schedule can be defined as a chronological order of execution of multiple transactions. There are broadly two types of transaction schedules Serial Schedule Non-Serial Schedule
- 5. 5 i) Serial Schedule • In this kind of schedule, when multiple transactions are to be executed, they are executed serially, i.e. At one time only one transaction is executed while others wait for the execution of the current transaction to be completed. This ensures consistency in the database as transactions do not execute simultaneously. • But, it increases the waiting time of the transactions in the queue, which in turn lowers the throughput of the system, i.e. Number of transactions executed per time. • To improve the throughput of the system, another kind of schedule are used which has some more strict rules which help the database to remain consistent even when transactions execute simultaneously.
- 6. 6 ii) Non-Serial Schedule To reduce the waiting time of transactions in the waiting queue and improve the system efficiency, we use non serial schedules which allow multiple transactions to start before a transaction is completely executed. This may sometimes result in inconsistency and errors in database operation. So, these errors are handled with specific algorithms to maintain the consistency of the database and improve CPU throughput as well. • Non-serial schedules are also sometimes referred to as parallel schedules, as transactions execute in parallel in these kinds of schedules.
- 7. Subject Code 7 TYPES OF TRANSACTIONS • Read-only Transactions: • Only retrieves data without making any changes. • Update Transactions: • Modifies existing data in the database. • Insert Transactions: • Adds new records to the database. • Delete Transactions: • Removes data from the database. • Complex Transactions: • Includes multiple types of operations in a single transaction.
- 8. 8 States of transaction A transaction is a series of operations, so various states occur in its completion journey.
- 9. TRANSACTION STATES • Active: • The transaction is being executed. • Partially Committed: • After the final operation is executed, but before the transaction is committed. • Committed: • The transaction has been successfully completed and changes are saved permanently. • Failed: • If any error occurs during execution, the transaction enters this state. • Aborted: • The transaction has been rolled back due to an error, and the database is restored to its previous state.
- 10. 10 Properties of transaction As transactions deal with accessing and modifying the contents of the database, they must have some basic properties which help maintain the consistency and integrity of the database before and after the transaction. Transactions follow 4 properties, namely, Atomicity, Consistency, Isolation, and Durability. Generally, these are referred to as ACID properties of transactions in DBMS. ATOMICITY This property ensures that either all operations of a transaction are executed or it is aborted. In any case, a transaction can never be completed partially. CONSISTENCY This property of a transaction keeps the database consistent before and after a transaction is completed. ISOLATION This property states that two transactions must not interfere with each other, i.e. If some data is used by a transaction for its execution, then any other transaction can not concurrently access that data until the first transaction has completed. DURABILITY This property ensures that the changes made to the database after a transaction is completely executed, are durable.
- 11. Subject Code 11 CONCURRENCY CONTROL • Concurrency control ensures that multiple transactions can execute in parallel without conflicting with each other. • Techniques include: • Locking: Locks data to prevent other transactions from accessing it simultaneously. • Timestamp Ordering: Assigns timestamps to transactions and processes them in timestamp order. • Optimistic Concurrency Control: Allows transactions to execute without restrictions and checks for conflicts at commit time.
- 12. Subject Code 12 TRANSACTION RECOVERY • Recovery ensures that the database is restored to a consistent state after a failure (e.g., power loss, system crash). • Techniques: • Rollback: If a transaction fails, it is rolled back to its original state. • Write-Ahead Logging (WAL): Logs are written to disk before the actual transaction data is committed to ensure recovery. • Shadow Paging: Uses a backup copy of the database pages to roll back if necessary
- 13. 13 Conclusion Transactions in DBMS are pivotal in maintaining the integrity and consistency of the database through a series of well-defined operations and states. From the initial execution of operations to handling errors and ensuring consistency, transactions must adhere to the ACID properties—Atomicity, Consistency, Isolation, and Durability. These properties guarantee that transactions are processed reliably and that the database remains stable even in the face of failures or concurrent operations.