02/23/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Transaction I

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Outline

Transaction and OLTP Designed properties of transactions

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Transaction

A multi-billion dollar business OLTP http://www.tpc.org/default.asp

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Transaction Definition

A unit of program execution that accesses and possibly updates various data items

Transactions? Book an airline ticket from DFW to Paris Buy “The Dilbert Principle” from amazon.com Sell 1000 shares of LU from your ameritrade account Withdraw $100 from a ATM machine Issue a SQL statement to sqlplus of Oracle 9i Look at your grade of homework 3 Check out your groceries at Walmart

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Challenges to Maintain Transactions

Hardware failures Cashed stuck in ATM machine Power failure…

Software failures Programming errors System crash…

User interference Termination of transactions

Concurrent users Multiple users accessing the same item

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Designed Properties of Database Systems

Atomicity Consistency Isolation Durability

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Atomicity

Transaction needs to be executed as a unit Example

You should not cause the quantity of “The Dilbert Principle” of amazon.com decrease if you place your order and the order does not get through due to server errors

Who are responsible for atomicity? Transaction management system and Recovery system

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Consistency

Database implicit/explicit constraints need to be maintained

Example: Transferring money from one account to another in the same

bank should not change your total amount of money

Who are responsible for consistency? Transaction management system and Programmer

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Isolation

Transaction A should not see partial results of transaction B

Analogy: When I update my website here and there, you should not see

and think a tentative version as my final version

Who are responsible for isolation? Transaction management system

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Durability

Any transaction committed needs to be in database for ever

Example: After you get the receipt of the water melon you buy from

Alberson, the transaction is final and permanently reflected in the database system If you want to cancel it, that is another transaction

Who are responsible for durability? Transaction management system and Recovery system

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Transaction’s State Diagram

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

An Ideal World

No hardware failures No software failures No programming errors Do we still need transaction management?

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Why Concurrent Transactions?

Parallelism Improved response time

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Schedule

Schedules – sequences that indicate the chronological order in which instructions of concurrent transactions are executed a schedule for a set of transactions must consist of all

instructions of those transactions must preserve the order in which the instructions appear in

each individual transaction.

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Example Schedules

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Example Schedule (Cont.)

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Example Schedules

1/14/2005 Yan Huang - CSCI5330 Database Implementation – Transaction

Concurrency Control

Some schedules are bad because the outcome of the schedule is not “predictable”