Introduction is not only for data access faster, but

Introduction

Distributed
database is a database in which storage devices are not all attached to a
common processing unit, but it is stored in multiple computers. In today’s
world of Information Technology, it is demand of society to available all
information on hand. In distributed database, users can access the information
at anywhere and anytime in the network. There is also requiring for secure and
reliable communication of information. The concurrency control and security
issues in distributed database have presented in this paper.

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Theory

Distributed
database systems provide an improvement on communication and data processing
due to its data distribution throughout different network sites. It is not only
for data access faster, but also a single-point of failure is less likely to
occur and it provides local control of data for users. A distributed database
is a single logical database that is spread physically across computers in
multiple locations that are connected by data communication links. The
advantage of distributed database is data is distributed, so that the network
traffic is reduced. If the company network is temporarily broken, the local
database does not affected and it will remain the works. The distributed
database is stored in multiple computers, so that it will not affect the work
of other branch when there is problems occur in one branch. However, it is more
complex to make sure that the data and indexes in distributed system are not
corrupted. It is not efficient when there is heavy interaction between sites
and security problem as data are distributed.

Literatures
review

The
design of distributed database is introduced into three issues: fragmentation,
replication and data allocation. According to the research of Shin and Irani
1, fragmentation is a design technique to divide a relation into two or more
partitions. There are several types of fragmentation which are horizontal,
vertical and hybrid fragmentation. For horizontal fragmentation, it is defined
as the selection operation. The divides table horizontally by selecting the
relevant rows and these fragments can be assigned to different sides in the
distributed system. For vertical fragmentation, it is defined using the
projection operation and it divides the relation into columns. It is necessary
to include the primary key of table in each vertical fragmentation for allowing
reconstruction. For hybrid fragmentation, it is also called mixed fragmentation
because it is the combination of both horizontal and vertical fragmentations.
This fragmentation is more complex than previous fragmentation because the
table is divided into arbitrary blocks based on requirement. Carlos and Steven
described that the data replication is refer to the storage of data copies at
multiple sites served by a computer network 2. The problem in managing
replicated data is to maintain the consistency of the data. Replicated data are
subject to the mutual consistency rule. The mutual consistency rule requires
that all copies of data fragments be identical. According to the research of
Swati, Kuntal and Bhawna 3, data Allocation is described as the process of
deciding where to locate data. Data allocation strategies are classified into centralized
data allocation, partitioned data allocation and replicated data allocation.

Result
outcome

Concurrency
control is the activity of processing concurrent accesses to a database in
distributed database system. Transaction is a set of read or writes operation
used to perform a unit of work. Hence, the database transaction must be atomic,
consistent, isolated and durable. There are some distributed concurrency
control technique have been discussed. Firstly, basic timestamp ordering
algorithm which is used to determine the out datedness of request with respect
to the data objects and to order events with respect to one another based on
their timestamp values. Timestamp is a unique identifier to identify a
transaction. The timestamp-ordering protocol ensures serializability among
transaction in their conflicting Read and Write operations 4. Next technique
is distributed two-phase locking (2PL). The main approach of the two phase
locking protocol is “read any, write all” 5. The 2PL Protocol oversees locks
by determining when transactions can acquire and release locks. Each
transaction executed in two phases which are growing phase and shrinking phase.
Lock managers are distributed to all sites and each responsible for locks for
data at that.  Besides that, distributed
optimistic protocol (OPT) is operates by exchanging certification information
during the commit protocol. The transaction is assigned a globally unique
timestamp when all the transaction’s cohorts completed their work and reported
back to the master. This time stamp is sent to each cohort in the “prepare to
commit” message and it is used to locally certify all of its reads and writes
6. On the other hand, security is used to protect data or information from
modification and unauthorized access. There are five approaches in security
aspect of client and server. First, the work station approval mechanism of
users may be partial or non-existent. It is possible to carry out automation of
the Login procedure. Next, the work station may be installed in a public area
or in a high risk area. The work station may active strong utilities or
development devices and thereby tries to bypass the security mechanism. In
extreme cases the users may pretend to be another user and infiltrate the
system.  Security authentication,
authorization, encryption and access control is the main security for
distributed database system. Deadlock is the major problem in distributed
system. It is the state of process where set of process are waiting for each
other 7.

Conclusion

Fragmentation,
replication and data allocation are important issues for designing the
distributed database. The basic concept of concurrency control in distributed
database systems and the various techniques for concurrency control in
distributed environments are discussed. The need for distributed database in
today’s business environment has been increasing. Hence, it is important to
ensure that the system operate in a secure environment and integrity. Deadlock
is the major problem in distributed database. Hence, we need to find out the
methods to data distribution and accessing which leads to minimization of
deadlock and thus resulting in proper utilization of resources.