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Transcript 
Database Processing
Chapter 12
Managing Multi-user Databases
David M. Kroenke
© 2000 Prentice Hall
Chapter 12
Multi-User Issues
•
•
•
•
Concurrency Control
Database Reliability
Database Security
Database Administration
Page 307
© 2000 Prentice Hall
Chapter 12
Common Multi-User DBMS
• Windows 2000
– Access 2000
– SQL Server
– ORACLE
Page 307
• UNIX
– ORACLE
– Sybase
– Informix
© 2000 Prentice Hall
Chapter 12
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
© 2000 Prentice Hall
Chapter 12
Concurrent Processing
Problems
• Lost update problem
• Inconsistent read problem
Page 312
© 2000 Prentice Hall
Chapter 12
Remedy for inconsistencies caused
by concurrent processing
• Resource Locking
“disallow sharing by locking data that
are retrieved for update”
Page 312
© 2000 Prentice Hall
Chapter 12
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
Page 312
© 2000 Prentice Hall
Chapter 12
Serializable Transactions
“a scheme for processing concurrent
transactions”
Strategies
– two-phased locking
– COMMIT and ROLLBACK commands
Page 313
© 2000 Prentice Hall
Chapter 12
Deadlock
“deadly embrace”; each transaction
waiting for a resource that the other
person has locked
Page 314
© 2000 Prentice Hall
Chapter 12
Lock Styles
Optimistic assumption is made that no
conflict will occur
Pessimistic assumption is made that
conflict will occur
Page 314
© 2000 Prentice Hall
Transaction Isolation Levels
Page 317
Figure 12-8
© 2000 Prentice Hall
Summary of Cursor Types
Page 319
Figure 12-9
© 2000 Prentice Hall
Chapter 12
Database Recovery
• Via Reprocessing
• Via Rollback/Rollforward
Page 320
© 2000 Prentice Hall
Chapter 12
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
© 2000 Prentice Hall
Database Security
Page 324
Figure 12-13
© 2000 Prentice Hall
Model of ORACLE Security
Page 325
Figure 12-14a
© 2000 Prentice Hall
Model of SQL Server Security
Page 327
Figure 12-15a
© 2000 Prentice Hall
Chapter 12
Database Administration
• DBA database administrator
–
–
–
–
manages
manages
manages
manages
Page 329
the database structure
data activity
the DBMS
the data repository
© 2000 Prentice Hall
Chapter 12
Managing the Database Structure
• Configuration Control
• Documentation
Page 330
© 2000 Prentice Hall
Managing the Database Structure
Page 331
Figure 12-16
© 2000 Prentice Hall
Chapter 12
Managing Data Activity
Data dictionary names and formats of
the data items, and their
relationships
Data proponents key database users
Page 331
© 2000 Prentice Hall
Managing Data Activity
Page 332
Figure 12-17
© 2000 Prentice Hall
Managing the DBMS
Page 333
Figure 12-18
© 2000 Prentice Hall
Chapter 12
Managing the Data Repository
Data repositories collections of
metadata about databases, database
applications, Web pages, users, and
other application components
– active
– passive
Page 334
© 2000 Prentice Hall
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