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
Provide Examples of different types of Time and Date formats.  It's most common store dates using a dash (-) as a colon (:)and the delimiter as the time delimiter. The given fo


What is an Index? An index is a small table having only two columns. The first column has a copy of the primary or candidate key of a table and the second column having a set o

This constraint shows that the key attribute value in each tuple must be unique, i.e., no two tuples have the similar value for the key attribute. This is because the value of the

how many hourse have been spent on a certain project

The Database Approach In order to overcome the limits of a file system, a new approach was needed. Hence a database approach emerged. A database is a persistent collection of

Project Description: Need Point of Sale software for pizza restaurant. Delivery and take out service, client's database, inventory control, order history, last order, order from

Implementing software control To implement software control designer must redesign strategy of state event model which is present in dynamic model. There are three basic ap

What is an index? An index is a structure that helps to place desired records of a relation quickly, without probing all records.

Explain the Natural join Natural join is a binary operator which is written as (R* S) in which R and S are relations. The effect of the natural join is the set of all combinati