1. Introduction of Week 13 Return assignment 11-1 and 3-1-5
Collect assignment Questions?
Review of week 12
DBA activities
Oracle DBMS tools
Oracle data dictionary
Privileges
Database Management Systems

2. Module 6 Advanced Database Concepts
Section 2: Transaction Processing
Module 6 Advanced Database Concepts

3. DML Action
Simple SELECT statement to generate a list of table contents
A series of related UPDATE statements to change the values of attributes in various tables
A series of INSERT statements to add rows to one or more tables
A combination of SELECT, UPDATE, and INSERT statements
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4. Transaction
A logical unit of work that must be either entirely completed or aborted
Successful transaction changes the database from one consistent state to another, in which all data integrity constraints are satisfied
Most real-world database transactions are formed by two or more database DML requests
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5. Transaction Properties
Atomicity - all operations (SQL requests) of a transaction be completed
Durability – indicates permanence of database’s consistent state
Serializability - ensures that the concurrent execution of several transactions yields consistent results
Isolation - Data used during execution of a transaction cannot be used by second transaction until first one is completed
Database Management Systems

6. The Transaction Log A record for the beginning of transaction
For each transaction component (SQL statement)
Type of operation being performed (update, delete, insert)
Names of objects affected by the transaction (the name of the table)
“Before” and “after” values for updated fields
Pointers to previous and next transaction log entries for the same transaction
The ending (COMMIT) of the transaction
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7. A Transaction Log
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8. Database Audit Trail
From the backup and logs, databases can be restored in case of damage or loss
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9. Concurrency Control
Coordination of simultaneous transaction execution in a multiprocessing database system
Objective is to ensure transaction serializability in a multiuser database environment
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10. Concurrency Control
Important  simultaneous execution of transactions over a shared database can create several data integrity and consistency problems
lost updates
uncommitted data
inconsistent retrievals
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11. Lost Updates: Normal Execution
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12. Lost Updates: Concurrency Problem
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13. Uncommitted Data: Correct Executions
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14. Uncommitted Data: Concurrency Problem
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15. Inconsistent Retrievals: Two Transactions
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16. Inconsistent Retrievals: Correct Transaction Results
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17. Inconsistent Retrievals: Concurrency Problem
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18. The Scheduler
Special DBMS program: establishes order of operations within which concurrent transactions are executed
Interleaves the execution of database operations to ensure serializability and isolation of transactions
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19. The Scheduler (continued)
Bases its actions on concurrency control algorithms
Ensures computer’s central processing unit (CPU) is used efficiently
Facilitates data isolation to ensure that two transactions do not update the same data element at the same time
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20. Conflicting Database Operations Matrix
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21. Concurrency Control with Locking Methods
Guarantees exclusive use of a data item to a current transaction
Required to prevent another transaction from reading inconsistent data
Lock manager
Responsible for assigning and policing the locks used by the transactions
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22. Updates with locking for Concurrency Control
This prevents the lost update problem
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23. Lock Granularity Indicates the level of lock use
Locking can take place at the following levels:
Database
Table
Block or page
Record (row)
Field (attribute)
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24. Lock Types Binary lock Exclusive lock Shared lock
Has only two states: locked (1) or unlocked (0)
Exclusive lock
Access is specifically reserved for the transaction that locked the object
Must be used when the potential for conflict exists
Shared lock
Concurrent transactions are granted Read access on the basis of a common lock
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25. An Example of a Binary Lock
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26. Two-Phase Locking to Ensure Serializability
Defines how transactions acquire and relinquish locks
Guarantees serializability, but it does not prevent deadlocks
Growing phase, in which a transaction acquires all the required locks without unlocking any data
Shrinking phase, in which a transaction releases all locks and cannot obtain any new lock
Database Management Systems

27. Two-Phase Locking to Ensure Serializability (continued)
Governed by the following rules:
Two transactions cannot have conflicting locks
No unlock operation can precede a lock operation in the same transaction
No data are affected until all locks are obtained—that is, until the transaction is in its locked point
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28. Two-Phase Locking Protocol
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29. Deadlocks
Condition that occurs when two transactions wait for each other to unlock data
Possible only if one of the transactions wants to obtain an exclusive lock on a data item
No deadlock condition can exist among shared locks
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30. How a Deadlock Condition Is Created
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31. Deadlocks Control
Prevention – a transaction requesting a new lock is aborted if it might cause a deadlock
Detection
Allow deadlocks to occur
Mechanisms for detecting and breaking them, such as resource usage matrix
Avoidance – a transaction must obtain all the locks it needs before it can be executed.
Database Management Systems

32. Concurrency Control with Time Stamping Methods
Assigns a global unique time stamp to each transaction
Produces an explicit order in which transactions are submitted to the DBMS
Uniqueness - ensures that no equal time stamp values can exist
Monotonicity - ensures that time stamp values always increase
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33. Deadlock Resolution Schemes
Wait/die - older transaction continues and the younger is rolled back
Wound/wait - older transaction rolls back the younger transaction continues
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34. Concurrency Control with Optimistic Methods
Based on the assumption that the majority of database operations do not conflict
Does not require locking or time stamping techniques
Transaction is executed without restrictions until it is committed
Phases are read, validation, and write
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35. Database Recovery Management
Restores database from a given state, usually inconsistent, to a previously consistent state
Based on the atomic transaction property - all portions of the transaction must be treated as a single logical unit of work
If transaction operation cannot be completed, transaction must be aborted, and any changes to the database must be rolled back
Database Management Systems

36. Database Backup Level of backup Failures that plague databases
Full backup
Differential backup, incremental backup
Transaction log backup
Failures that plague databases
Software – OS, DBMS, applications
Hardware – memory errors, disk crashes
Human errors
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37. Wrap Up
No new assignment!
Database Management Systems