24-09-2013, 03:55 PM
Transaction Processing Concepts
Transaction Processing .ppt (Size: 1.04 MB / Downloads: 78)
Introduction to Transaction Processing
Single-User Vs. Multi-User Systems
Read and Write Operations of a Transaction
Problems in Concurrency Operations
Types of Transaction Failures
Serializability of Schedules
Single-User Vs. Multi-User System
A DBMS is single-user if at most one user at a time can use the system
A DBMS is multi-user if many user can use the system concurrently
In a multi DBMS, the stored data items are the primary resources that may be accessed concurrently by user programs, which are constantly retrieving information from and modifying the database. The execution of a program that accesses or change the contents of the database is called a transaction.
Objectives
Function and importance of transactions.
Properties of transactions.
Concurrency Control
Meaning of serializability.
How locking can ensure serializability.
Deadlock and how it can be resolved.
How timestamping can ensure serializability.
Optimistic concurrency control.
Granularity of locking.
Transaction Support
Transaction
Action, or series of actions, carried out by user or application, which accesses or changes contents of database.
Logical unit of work on the database.
Application program is series of transactions with non-database processing in between.
Transforms database from one consistent state to another, although consistency may be violated during transaction. (If the system crashes, each transaction's changes are reflected in the persistent database either entirely or not at all.)
Transaction Support
Can have one of two outcomes:
Success - transaction commits and database reaches a new consistent state.
Failure - transaction aborts, and database must be restored to consistent state before it started.
Such a transaction is rolled back or undone.
Committed transaction cannot be aborted.
Aborted transaction that is rolled back can be restarted later.
Concurrency Control
Process of managing simultaneous operations on the database without having them interfere with one another.( Centralized system with concurrent access by several users)
Prevents interference when two or more users are accessing database simultaneously and at least one is updating data.
Although two transactions may be correct in themselves, interleaving of operations may produce an incorrect result.