CLIENT/SERVER DATABASE AND DISTRIBUTED DATABASE - Fundamentals of Database Management Systems - page 329

copies of Tables E and F, respectively? Because the distance (and probably the cost)
between Memphis and New York is much less than the distances involving Paris
and Tokyo. Finally, what about the option of shipping the data needed from both
tables to Los Angeles, the city that issued the query, for execution? Remember, the
entirety of Table F is needed for the join in this example. Shipping all of Table F
to Los Angeles to execute the join there would probably be much more expensive
than the New York option.

Partitioning or Fragmentation
Another option in the distributed database bag-of-tricks is known as '' partitioning ''
or '' fragmentation .'' This is actually a variation on the theme of file partitioning
that we discussed in the context of physical database design.
In horizontal partitioning, a relational table can be split up so that some
records are located at one site, other records are located at another site, and so on.
Figure 12.10 shows the same five-city network we have been using as an example,
with another table, Table G, added. The figure shows that subset G1 of the records
of Table G is located in Memphis, subset G2 is located in Los Angeles, and so on.
A simple example of this would be the company's employee table: the records of
the employees who work in a given city are stored in that city's computer. Thus,
G1 is the subset of records of Table G consisting of the records of the employees

ASIA

Tokyo

EUROPE

ARCTIC
OCEAN A F

G5

U.K.

GREENLAND
(DEN.)

Paris

B D E

G4

AFRICA

CANADA

A B F

C D

NORTH AMERICA

G3

PACIFIC
OCEAN

ATLANTIC
OCEAN G2

New York

UNITED STATES
Memphis

Los Angeles

D E

G1

MEXICO

Caribbean
Sea

SOUTH AMERICA

F I G U R E 12.10
Distributed database with data
partitioning/fragmentation