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Chapter 12 Managing Multi-user Databases David M. Kroenke Database Processing © 2000 Prentice Hall
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Chapter 12
Managing Multi-user Databases
David M. Kroenke
Database Processing
© 2000 Prentice Hall
Chapter 12
© 2000 Prentice Hall
Multi-User Issues
• Concurrency Control• Database Reliability• Database Security• Database Administration
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Common Multi-User DBMS
• Windows 2000– Access 2000– SQL Server– ORACLE
• UNIX– ORACLE– Sybase– Informix
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Concurrency Control
“making sure that one user’s work does not inappropriately influence another’s”
The need for atomic transactions “logical work performed as a unit”
Page 308
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Concurrent Processing Problems
• Lost update problem• Inconsistent read problem
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Remedy for inconsistencies caused by concurrent
processing• Resource Locking“disallow sharing by locking data
that are retrieved for update”
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Lock Terminology
• Implicit locks placed by the DBMS• Explicit locks placed by command• Lock granularity the size of the lock• Exclusive lock from access of any type• Shared lock from change but not read
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Serializable Transactions
“a scheme for processing concurrent transactions”
Strategies– two-phased locking– COMMIT and ROLLBACK
commands
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Deadlock
“deadly embrace”; each transaction waiting for a resource that the other person has locked
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Lock Styles
Optimistic assumption is made that no conflict will occur
Pessimistic assumption is made that conflict will occur
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Transaction Isolation Levels
Page 317Figure 12-8 © 2000 Prentice Hall
Summary of Cursor Types
Page 319Figure 12-9© 2000 Prentice Hall
Chapter 12
© 2000 Prentice Hall
Database Recovery
• Via Reprocessing• Via Rollback/Rollforward
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Recovery Terminology
Log records of the data changes in chronological order
Before-images/After-images copy of every record before / after it was changed
Checkpoint a point of synchronization between the database and the transaction log
Page 321
Database Security
Page 324Figure 12-13 © 2000 Prentice Hall
Model of ORACLE Security
Page 325Figure 12-14a © 2000 Prentice Hall
Model of SQL Server Security
Page 327Figure 12-15a © 2000 Prentice Hall
Chapter 12
© 2000 Prentice Hall
Database Administration
• DBA database administrator– manages the database structure– manages data activity– manages the DBMS– manages the data repository
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Managing the Database Structure
• Configuration Control• Documentation
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Managing the Database Structure
Page 331Figure 12-16 © 2000 Prentice Hall
Chapter 12
© 2000 Prentice Hall
Managing Data Activity
Data dictionary names and formats of the data items, and their relationships
Data proponents key database users
Page 331
Managing Data Activity
Page 332Figure 12-17 © 2000 Prentice Hall
Managing the DBMS
Page 333Figure 12-18 © 2000 Prentice Hall
Chapter 12
© 2000 Prentice Hall
Managing the Data Repository
Data repositories collections of metadata about databases, database applications, Web pages, users, and other application components– active– passive
Page 334
