1. Multi-User Databases
Chapter 9

2. Terminology Data administration Database administration
Database administrator or DBA
Facilitates the development and use of the database
Balances the conflicting goals of
Protecting the database
Maximizing its availability and benefit to users
1. Refers to a function that applies to an entire organizations
Is a management oriented functions
It is concerted with corporate data privacy and security issues
2. Is concerned with technical issues specific to a particular database includeing applications that process the database
3. Refers to the office or the manager

3. Tasks of DBA

4. Managing Database Structure
Participating in initial database design
Participating in initial database implementation
Controlling and managing changes to the database
Developing procedures and policies by which users an register their needs for changes
Documenting the database structure
Documnent: changes, when they were made, record of test procedures and test runs

5. Summary of DBA’s responsibilities for managing database structure

6. Problems

7. Solution

8. Transactions Transactions Logical units of work Atomic
Logical Units of work - suppose have three actions to occur when recording a new order and only 2 happen because of insufficient file space… either all three should be done or none.
Customer: increase amount due
Salesperson : increase commission due
Insert new order row into database
Atomic is a synonym

9. Concurrency Control
Needed to ensure that one user’s work does not interfere with another
Concurrent transactions
Concurrent transactions are not simultaneous
They are interleaved

10. Processing different data
Processing different data – no problem

11. Processing Same Data Look at order or processing
Potential problem of LOST UPDATE or CONCURRENT UPDATE
Another potential problem is the INCONSISTENT READ PROBLEM
User A reads data that have been processed by a PORTION of a transaction.

12. Resource Locking

13. Locks Implicit Explict Lock granularity Lock types Lock styles
Desired results
Implicit – done by database
Explicit – placed by command
Lock granularity – groups of rows within a table, the whole table, the whole dataabase
large granularity is easy to administer but cause conflicts
small granularity – difficult to administer but fewer conflicts
Lock types
exclusive – locks item from ANY other access
Shared lock – locked from change but not from read
Desirable results
Serializable – results same as if they had been processed sequentially
achieved by two-phased locking – obtain locks as needed but as soon as one released no others can be obtained – GROWING phase when locks are obtained SHRINKING phase when locks are released
Optimistic – assumes no conflict will occur
Pessimistic – conflict will occur – locks are issued and then freed

14. Deadlock – Deadly embrace
Deadlock: prevention, detection, correction
DBMS has algorithms for breaking deadlock
Need to detect
Need to get rid of deadlock - correct
Generally cancel one of transactions

15. Optimistic Locking

16. Pessimistic locking

17. Transaction Boundaries

18. Some useful terminology
Transaction-level consistency
Dirty read
Nonrepeatble reads
Phantom reads
Isolation levels – see figure 9-10
Scrollable cursor
Static cursor
Keyset
Dynamic cursor

19. Database Security Illustration
Rights
Responsibilities

20. Database Recovery Recovery via reprocessing
Recovery via rollback/rollforward
Necessity for a log