Read-set(t) and timestamps-optimistic concurrency contents, Database Management System

  • read-set(T): Each data items that are read by a transaction T
  • Timestamps: for all transaction T, the start-time and the end time are reserved for all the three phases.

Let us show this scheme here with the help of the following examples:

Consider the set for transaction T1 and T2.

T1

T2

Phase

Operation

Phase

Operation

-

-

Read

Reads the read set (T2). Let say variables X and Y and

performs updating of local values

Read

Reads the read set (T1) lets

say variable X and Y and performs updating of local values

-

-

Validate

Validate the values of (T1)

-

-

-

-

Validate

Validate the values of (T2)

Write

Write the updated values in

the database and commit

-

-

-

-

Write

Write the updated values in the

database and commit

In this given instance both T1 and T2 get committed. Please note that Read set of T1 and Read Set of T2 are both disjoint, also the Write sets are also disjoint and therefore no concurrency related problem can happen.

T1

T2

T3

Operation

Operation

Operation

Read R(A)

--

--

--

Read R(A)

--

--

--

Read (D)

--

--

Update(D)

--

--

Update (A)

 

--

 

--

Validate (D,A) finds OK

Write (D,A), COMMIT

 

--

Validate(A):Unsuccessful

Value changed by T3

 

--

Validate(A):Unsuccessful

Value changed by T3

 

--

 

--

ABORT T1

--

--

--

Abort T2

--

In this scheme both T1 and T2 get aborted as they fail during validate phase whereas only T3 is committed. Optimistic concurrency control performs its checking at the transaction commits point in a validation phase. The serialization order is defined by the time of transaction validation phase.

Posted Date: 3/12/2013 3:14:45 AM | Location : United States







Related Discussions:- Read-set(t) and timestamps-optimistic concurrency contents, Assignment Help, Ask Question on Read-set(t) and timestamps-optimistic concurrency contents, Get Answer, Expert's Help, Read-set(t) and timestamps-optimistic concurrency contents Discussions

Write discussion on Read-set(t) and timestamps-optimistic concurrency contents
Your posts are moderated
Related Questions
Explain the concepts of relational data model? Relational Data Model - The relational model was first introduced through Prof. E.F. Codd of the IBM Research in the year 1970

What is Data dictionary? A data dictionary is a reserved space in a database that is employed to store information about the database itself. A data dictionary may consist o

Question 1 Create a table student with attributes student name, roll number, total marks and percentage. Do the following operations Insert details in to the table Update


Describe analysis of access paths To describe analysis of access paths, consider an example of the design of a company's employee skills database. A part of the object model fr

In an organisation various projects are undertaken. Each projects can employ one or more employees. Every employee can work on one or more projects. Each project is undertaken on

Determine Which is not a consequence of concurrent operations? Ans: Update anomaly.

What is Structured Query Langauge (SQL)? SQL is a powerful set-oriented language which was formed by IBM research for the databases that adhere to the relational model. It havi

Data Mining 1. What is data mining? Write Data Mining applications. 2. Explain OLAP? Write the benefits of OLAP. 3. What are the key features of a Data Warehouse? 4. W

State the meaning of Object Representation  The term object representation means "to represent object with the help of objects model symbols". Implementing objects is too simp