Serialisable schedules, Database Management System

Serialisable Schedules:If the processes of two transactions conflict with each other, how to verify that no concurrency related problems have happened? For this, serialisability theory has been developed. Serialisability theory attempts to verify the correctness of the schedules. The rule of this theory is:

"A schedule S of n transactions is serialisable if it is equal to some serial schedule of the similar 'n' transactions".

A serial schedule is a schedule in which either transaction T1 is totally done before T2 or transaction T2  is totally done before T1. For instance, the following figure clears the two possible serial schedules of transactions T1  & T2.

Schedule A: T2 followed by T1

Schedule B: T1 followed by T2

Schedule

T1

T2

Schedule

T1

T2

Read X

 

Read X

Read X

Read X

 

Read Y

 

Read Y

Subtract 100

Subtract 100

 

Display X+Y

 

Display X+Y

Write X

Write X

 

Read X

Read X

 

Read Y

Read Y

 

Subtract 100

Subtract 100

 

Add 100

Add 100

 

Write X

Write X

 

Write Y

Write Y

 

Read Y

Read Y

 

Read X

 

Read X

Add 100

Add 100

 

Read Y

 

Read Y

Write Y

Write Y

 

Display X+Y

 

Display X+Y

                                                                         Figure: Serial Schedule of two transactions

Schedule C: An Interleaved Schedule

Schedule

T1

T2

Read X

Read X

 

Subtract 100

Subtract 100

 

Read X

 

Read X

Write X

Write X

 

Read Y

 

Read Y

Read Y

Read Y

 

Add 100

Add 100

 

Display X+Y

 

Display X+Y

Write Y

Write Y

 

                                                                           Figure: An Interleaved Schedule

Now, we have to figure out whether this interleaved schedule would be performing read and write in the same order as that of a serial schedule. If it does, then it is equivalent to a serial schedule, otherwise not. In case it is not equivalent to a serial schedule, then it may result in problems due to concurrent transactions.

Posted Date: 3/12/2013 2:00:21 AM | Location : United States







Related Discussions:- Serialisable schedules, Assignment Help, Ask Question on Serialisable schedules, Get Answer, Expert's Help, Serialisable schedules Discussions

Write discussion on Serialisable schedules
Your posts are moderated
Related Questions
What are the benefits of prepared statements and place holders? Parameter binding operations automatically handle escaping of characters Encourage Statement reuse

Describe the advantage of State chart Diagram A state chart represents a state machine, emphasizing flow of control from one state to other. A state machine is a behaviour whi

what are the states of transaction?

What was the method in which records are physically stored in a specified order according to a key field in each record ? A method in which records are physically stored within

Explain trigger? Trigger: A database trigger is procedural code which is automatically executed within response to certain events on a particular table in a database. Trigger

There are a number of possible solutions to the open ended brief. One of the simple ones is shown here without the PKs and FKs. It is important to think of how a number of tasks

i need help for assignment ..

Automated system for appointment with sms and call confirmation with service providers and user has to be initiate automatically. After selecting time and date to use service, s

State the Steps of Object Design Object design is a very iterative process in which various classes, relationships among objects are added when you move from one level to

Hashed File Organisation Hashing is the most common form of purely random access to a database or file. It is also used to access columns that do not have an index as an optimi