Fragmentation in Distributed DBMS

Fragmentation is a course of isolating the entire or full information base into different sub tables or sub relations with the goal that information can be put away in various frameworks. The little bits of sub relations or sub tables are called sections. These parts are called sensible information units and are put away at different locales. It should be ensured that the sections are with the end goal that they can be utilized to reproduce the first connection (i.e., there isn't any deficiency of information).

In the fragmentation cycle, suppose, If a table T is divided and is separated into various sections say T1, T2, T3… .TN. The sections contain adequate data to permit the reclamation of the first table T. This rebuilding should be possible by the utilization of UNION or JOIN procedure on different pieces. This interaction is called information fragmentation. These parts are free which implies these pieces cannot be gotten from others. The clients shouldn't need to be coherently worried about fragmentation which implies they ought not worried that the information is divided and this is called fragmentation Independence or we can say fragmentation straightforwardness.


  • As the information is put away near the utilization site, the proficiency of the data set framework will increase
  • Neighborhood question advancement strategies are adequate for certain inquiries as the information is accessible locally
  • To keep up with the security and protection of the data set framework, fragmentation is favorable


  • Access velocities might be extremely high on the off chance that information from various sections is required
  • In the event that we are utilizing recursive fragmentation, it will be extravagant

We have three strategies for information dividing of a table

  • Level fragmentation
  • Vertical fragmentation
  • Blended or Hybrid fragmentation

We should talk about them individually.

Horizontal fragmentation -

Horizontal fragmentation refers to the method involved with isolating a table evenly by appointing each line or (a gathering of columns) of connection to at least one pieces. These pieces are then be allotted to various sides in the dispersed framework. A portion of the columns or tuples of the table are set in one framework and the rest are put in different frameworks. The lines that have a place with the flat parts are indicated by a condition on at least one credits of the connection. In social variable-based math level fragmentation on table T, can be addressed as follows:


where, σ is social variable-based math administrator for determination

p is the condition fulfilled by an even part

Note that an association activity can be performed on the parts to develop table T. Such a section containing every one of the columns of table T is known as a total even part.

For instance, consider an EMPLOYEE table (T) :

Eno     Ename            Design            Salary             Dep

101     A                     abc                  3000               1

102     B                     abc                  4000               1

103     C                     abc                  5500               2

104     D                     abc                  5000               2

105     E                      abc                  2000               2

This EMPLOYEE table can be partitioned into various pieces like:

EMP 1 = σDep = 1 EMPLOYEE

EMP 2 = σDep = 2 EMPLOYEE

These two sections are: T1 part of Dep = 1

Eno     Ename            Design            Salary             Dep

101     A                     abc                  3000               1

102     B                     abc                  4000               1

Likewise, the T2 section based on Dep = 2 will be :

Eno     Ename            Design            Salary             Dep

103     C                     abc                  5500               2

104     D                     abc                  5000               2

105     E                      abc                  2000               2

Presently, here it is feasible to get back T as T = T1 T2 … . TN

Vertical Fragmentation

Vertical fragmentation alludes to the most common way of decaying a table upward by credits are sections. In this fragmentation, a portion of the traits are put away in one framework and the rest are put away in different frameworks. This is on the grounds that each site may not require all segments of a table. To deal with rebuilding, each section should contain the essential key field(s) in a table. The fragmentation should be in such a way that we can modify a table from the section by taking the normal JOIN activity and to make it potential we want to incorporate an exceptional property called Tuple-id to the construction. For this reason, a client can utilize any really key. Furthermore, by this, the tuples or lines can be connected together. The projection is as per the following:

πa1, a2,…, an (T)

where, π (algebra operator)

a1… ., an are the attributes of T

T is the table (relation)

For instance, for the EMPLOYEE table we have T1 as :

Eno     Ename            Design            Tuple_id

101     A                     abc                  1

102     B                     abc                  2

103     C                     abc                  3

104     D                     abc                  4

105     E                      abc                  5

For the second. sub table of connection after vertical fragmentation is given as follows :

Salary             Dep                 Tuple_id

3000               1                      1

4000               2                      2

5500               3                      3

5000               1                      4

2000               4                      5

This is T2 and to return to the first T, we join these two parts T1 and T2 as πEMPLOYEE (T1 T2)

Mixed Fragmentation

The blend of vertical fragmentation of a table followed by additional even fragmentation of certain parts is called blended or half and half fragmentation. For characterizing this kind of fragmentation we utilize the SELECT and the PROJECT tasks of social polynomial math. In certain circumstances, the level and the upward fragmentation isn't to the point of conveying information for certain applications and in that circumstances, we want a fragmentation called a blended fragmentation.

Blended fragmentation should be possible in two unique ways:

  1. The first technique is to initially make a set or gathering of even pieces and afterward make vertical parts from at least one of the level sections.
  2. The second technique is to initially make a set or gathering of vertical parts and afterward make level sections from at least one of the upward pieces.

The first connection can be gotten by the blend of JOIN and UNION tasks which is given as follows:

σP(πa1, a2..,an(T))

πa1,a2… .,an (σp(T))

For instance, for our EMPLOYEE table, underneath is the execution of blended fragmentation is πEname, Design (σEno < 104(EMPLOYEE))

The aftereffect of this fragmentation is:

Ename            Design

A                     abc

B                     abc

C                     abc