Serialisable schedules, Database Management System

Assignment Help:

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.


Related Discussions:- Serialisable schedules

Why dml is used for, Why DML is used for? DML is used to Manipulation and...

Why DML is used for? DML is used to Manipulation and processing of database. DML is provided for manipulation & processing of database. (Data stored in the database is processed

Replicating data, Replicating Data One approach that may support effici...

Replicating Data One approach that may support efficient access to dissimilar applications as above may be to give access to every of the applications from dissimilar replicate

Keys - relational database integrity, Candidate Key:  In a relation R, a ca...

Candidate Key:  In a relation R, a candidate key for R is a subset of the set of attributes of R, which have the differnt two properties: (1)        Uniqueness:                N

Define weak and strong entity sets, Define weak and strong entity sets?  ...

Define weak and strong entity sets?  Weak entity  set:  entity  set  that  do not  have  key  attribute  of  their  own are  known as weak entity sets.  Strong entity set

Production management, create an er diagram for production management in fi...

create an er diagram for production management in film industry

A table joined with itself is called, A table joined with itself is called ...

A table joined with itself is called ? A table joined with itself is known as self join table. Normal 0 false false false EN-IN X-NONE X-NONE

What are partial and natural key, What are partial, alternate,, artificial,...

What are partial, alternate,, artificial, compound and natural key? Partial Key: It is a set of attributes that can uniquely recognize weak entities and that are related to s

Naïve bayesian approach-id3 algorithm, You are working for the ABC Telecom ...

You are working for the ABC Telecom and are given some customer records for data mining. You are asked to discover, from the data, patterns that characterize low-, medium- and high

Define page, Define page. The database is partitioned into some number ...

Define page. The database is partitioned into some number of fixed-length blocks, which are referred to as pages.

Determine the programming language structures, What is the most significant...

What is the most significant feature that does not directly map into programming language structures? Why? Association, since there are complex types of association, like as qu

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd