1. CM603.21 Name : p.rajesh Year/Semester : VI Semester Subject : Advanced database system Subject Code : CM-603 Topic : Advanced database concepts Duration : 50 minutes Sub Topic : Transactions Properties Teaching Aids : Animation clips

2. CM603.22 Recap In this previous class, you have learnt about Basics of Transactions

3. CM603.23 OBJECTIVES: On completion of this period, you would be able to know Transactions Properties

4. CM603.24 Transactions and Concurrent Execution Transaction - DBMS’s abstract view of a user program (or activity): A sequence of reads and writes of database objects. Unit of work that must commit or abort as an atomic unit Transaction Manager controls the execution of transactions. User’s program logic is invisible to DBMS Arbitrary computation possible on data fetched from the DB The DBMS only sees data read/written from/to the DB.

5. CM603.25 Definitions Data Items—collection of objects representing a database. Granularity—size of a data item. Concurrency—multiple users accessing a database instance at the same time. Transaction—a logical unit of database processing that includes one or more database access operations from the following Insert, Delete, Modify, Retrieve operations Serializability—Interleaving execution of a set of concurrent transactions without “giving up any correctness”.

6. CM603.26 Definitions Concurrency Control Protocols—set of rules for defining the execution of concurrent transactions (ultimately to ensure serializability) Optimistic Concurrency Control—validation or certification of a transaction AFTER it executes If interference is detected, the transaction is aborted and restarted at a later time Contd…

7. CM603.27 Transaction Properties All transactions must display Atomicity, Consistency, Isolation, Durability and Serializability. These properties are referred to as ACIDS test

8. CM603.28 Atomicity Atomicity requires that all operations of a transaction must be completed. If not the transaction is aborted. If a transaction T1 has four SQL requests, all four requests must be successfully completed. Otherwise the entire transaction is aborted. –In other words, a transaction is treated as a single, indivisible, logical unit of work.

9. CM603.29 Consistency A transaction must transform the database from one consistent state to another consistent state. It is the responsibility of both the DBMS and the application programmers to ensure consistency. Consistency indicates the permanence of the database’s consistent state. When a transaction is completed the database reaches a consistent state.

10. CM603.210 Isolation: Transactions execute independently of one another. The partial effects of a transaction should not be visible to other transactions. Isolation means that the data used during the execution of a transaction cannot be used by a record transaction until the first one is completed. This property is useful in multi-user database environment because several different users can access and update the database at the same time

11. CM603.211 Durability Once a transaction is completed successfully, its results are recorded permanently in the database. They should not be lost because of any subsequent failures

12. CM603.212 Serializability A schedule is a list of operations by a set of concurrent transactions. A schedule is called serial when the operations of each transaction are executed consecutively without any interleaving. If there is any interleaving among the transaction then the schedule is non-serial.

13. CM603.213 When transactions are executed concurrently in a non-serial schedule is producing the same results as a serial schedule then the schedule is called serializable. A serial schedule never leaves the database in inconsistent state. Serializability is to find non-serial schedules, which can allow transactions to run concurrently with no interference and can produce correct results Serializability Contd…

14. CM603.214 Summary We have discussed about Transactions Properties- ACIDS

15. CM603.215 1. Transaction properties are also known as--- (a) DBMS (b) RDBMS (c) ACIDS (d) AIDS QUIZ

16. CM603.216 1. Transaction properties are also known as--- (a) DBMS (b) RDBMS (c) ACIDS (d) AIDS QUIZ

17. CM603.217 2. The property that transaction completed successfully is -- (a) serial (b) isolated (c) durability (d) atomicity QUIZ

18. CM603.218 (a) serial (b) isolated (c) durability (d) atomicity QUIZ 2. The property that transaction completed successfully is --

19. CM603.219 3. Serial schedule is ------ (a) physical (b) stream (c) multi (d) serializable QUIZ

20. CM603.220 3. Serial schedule is ------ (a) physical (b) stream (c) multi (d) serializable QUIZ

21. CM603.221 Questions 1. Explain Transaction properties?