chapters 16 and 17 - transaction processing

chapters 16 and 17 - transaction processing - COP 4710:...

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Unformatted text preview: COP 4710: Database Systems (Transaction Processing) Page 1 Mark Llewellyn COP 4710: Database Systems Fall 2007 CHAPTERS 16 & 17 Transaction Processing School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cop4710/fall2007 COP 4710: Database Systems (Transaction Processing) Page 2 Mark Llewellyn Introduction to Transaction Processing The execution of any program that either accesses (queries) or changes the database contents is called a transaction . Serial transactions two or more transactions are processed in serial fashion with one transaction starting and completing before the next transaction begins execution. At no time, is more than one transaction processing or making progress. Interleaved transactions two or more transactions are processed concurrently with only one transaction at a time actually making progress. This most often occurs on a single multi-programmed CPU. Simultaneous transactions two or more transactions are processed concurrently with any number progressing at one time. This is a multiple CPU situation. COP 4710: Database Systems (Transaction Processing) Page 3 Mark Llewellyn Introduction to Transaction Processing (cont.) t t 1 t 2 t 3 T3 T1 T2 time Serial transactions (unknown number of CPUs) COP 4710: Database Systems (Transaction Processing) Page 4 Mark Llewellyn Introduction to Transaction Processing (cont.) t t 2 t 4 t 6 T3 T1 T2 time Interleaved transactions (single CPU) t 1 t 5 t 3 T3 T2 T1 COP 4710: Database Systems (Transaction Processing) Page 5 Mark Llewellyn Introduction to Transaction Processing (cont.) t t 1 T1 time Simultaneous transactions (3 CPUs shown) T3 T2 COP 4710: Database Systems (Transaction Processing) Page 6 Mark Llewellyn Introduction to Transaction Processing (cont.) When viewed at the transaction level, any transaction has the potential to access the database in two ways: read(item): reads the value of some database item. write(item): write the value of an item into the database. These are not atomic operations. To read an item the following must occur: find the address of the disk block that contains the item. copy the disk block into buffer (if not already present). copy the item from the buffer into the program. COP 4710: Database Systems (Transaction Processing) Page 7 Mark Llewellyn Introduction to Transaction Processing (cont.) To write an item the following must occur: find the address of the disk block that contains the item. copy the disk block into buffer (if not already present)....
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This note was uploaded on 02/22/2009 for the course COP 4710 taught by Professor Dr. mark llewellyn during the Fall '07 term at University of Central Florida.

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chapters 16 and 17 - transaction processing - COP 4710:...

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