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CS411 - Transaction Management - Note 1 - 2

2 utilize while waiting on disk seeks cpu resources

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Unformatted text preview: hers Why Do We Learn This? (2 of 2) Transaction Management (5 of 61) E.g.: Imagine there are many users withdraw money from ATM. It needs to be completed simultaneously. We want to interleave. Interleaving: users and programs on top of our computing resource Why do we want to interleave? 1.Fairness: It’s about different users. Users are equally important. Users should feel they are the only one using the system. 2. Utilize: while waiting on disk seeks, CPU resources should allocate to other users. => Make sure that we are using our resources in an efficient way. Transactions Transactions (0 of 4) Transaction Management (6 of 61) Transaction - - - a unit of change in the database. Definition of "Transaction" Definition: A transaction is the execution of a DB program. • DB applications are designed as a set of transactions • Typical transaction • starts with data from user or from another transaction • includes DB reads/writes • ends with display of data or form, or with request to start another transaction Transactions (1 of 4) Transaction Management (7 of 61) It starts with data from user or from another transaction. Then the database will do some calculation such as adding the amount to be deposit. And at the end, with the display of data. - Jim Gray is the key person here Behind the Scene: Who invented Transaction? - More read here if you are interested: http://en.wikipedia.org/wiki/Jim_Gray_%28co mputer_scientist%29 • Edgar Codd? • Jim Gray? • Al Gore? Transactions (2 of 4) Transaction Management (8 of 61) Example: everything in reality is recorded on the database. If there is something changes in the reality, then the database need to be changed. This is transaction. Sumerians 6000 years ago invented writing for transaction processing on clay tablets Transactions (3 of 4) Transaction Management (9 of 61) And He is a Key Contributor Fundamental contributions to database and transaction processing. Defined the key transaction properties: atomicity, consistency, isolation and durability (ACID). From: Jim Gray at IBM: the transaction processing revolution. Bruce G. Lindsay. Transaction Management (10 of 61) Record. 37(2). June 2008. Transactions (4 of 4) ACM SIGMOD Correctness of Transactions Correctness of Transactions (0 of 12) Transaction Management (11 of 61) Atomicity • Transactions must be "atomic" • Their effect is all or none • DB must be consistent before and after the transaction executes (not necessarily during!) • EITHER • a transaction executes fully and "commits" to all the changes it makes to the DB • OR it must be as tho...
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