Processing & Properties of Floor and Wall Tiles.pptx
DBMS - Distributed Databases
1. Distributed Databases
A distributed database is a set of
interconnected databases that is distributed
over the computer network or internet.
It manages the distributed database and
provides mechanisms so as to make the
databases transparent to the users
2. Distributed Databases
Features
Databases in the collection are logically interrelated with
each other. Often they represent a single logical database.
Data is physically stored across multiple sites.
The processors in the sites are connected via a network.
A distributed database is not a loosely connected file
system.
3. Distributed Databases
Advantages:
Fast data processing
Reliability and availability
Reduced operating cost
Easier to expand
Improved sharing ability and local autonomy.
4. Distributed Databases
Disadvantages:
Complex to manage and control.
The security issues must be carefully managed
The system require deadlock handling during the
transaction processing
Need of standardization.
5. Distributed Databases
Homogeneous Distributed Database:
In this, all sites have identical database
management system software.
In such a system, local sites surrender a portion of
their autonomy in terms of their right to change
schemas or database management system software.
6. Distributed Databases
Homogeneous Distributed Database:
This software must also cooperate with other sites
in exchanging information about transactions, to
make transaction processing possible across
multiple sites.
It appears to user as a single system.
7. Distributed Databases
Heterogeneous Distributed Database:
In this, different sites may use different schemas, and
different database management system software.
The sites may not be aware of one another, and they
may provide only limited facilities for cooperation in
transaction processing.
8. Distributed Databases
Data Storage:
Replication: System maintains multiple copies of
data, stored in different sites, for faster retrieval
and fault tolerance
Fragmentation: Relation is partitioned into several
fragments stored in distinct sites
9. Distributed Databases
Data Replication:
The process of storing separate copies of the database
at two or more sites.
Full Replication: Entire relation is stored at all the
sites.
Partial Replication: Only some fragments of relation
are replicated on the sites.
11. Distributed Databases
Data Replication – Disadvantages:
Increased Storage Requirements
Increased Cost and Complexity of Data Updating
12. Distributed Databases
Data Fragmentation:
A division of relation r into fragments r1, r2,
r3…rn which contain sufficient information to
reconstruct relation r.
13. Distributed Databases
Data Fragmentation – Vertical Fragmentation:
The fields or columns of a table are grouped into
fragments.
In order to maintain reconstructiveness, each
fragment should contain the primary key field(s) of
the table.
14. Distributed Databases
Data Fragmentation – Vertical Fragmentation:
Example: Student(RollNo, Marks, City)
select RollNo from Student
select City from Student.
15. Distributed Databases
Data Fragmentation – Horizontal Fragmentation:
In this approach, each tuple of r is assigned to one or
more fragments.
If relation R is fragmentation in r1 and r2 fragments,
then to bring these fragments back to R we must use
union operation.
16. Distributed Databases
Data Fragmentation – Horizontal
Fragmentation:
Example:
Select * from student where marks>50 and
city=‘chennai’
18. Distributed Databases
Transaction Processing – Transaction
Manager:
Maintaining a log for recovery purposes
Participating in coordinating the concurrent
execution of the transactions executing at that site
19. Distributed Databases
Transaction Processing – Transaction
Coordinator:
Starting the execution of transactions that
originate at the site.
Distributing subtransactions at appropriate sites for
execution