Distributed DBMS

By :-Bharat P. Patil Bihag Mehta Ronak Thakkar Prashant Jaiswal

DISTRIBUTED DBMSDatabase:- Logical interrelated

collection of shared data, along with description of data, physically distributed over a computer network.

DBMS:- The software system that permits the management of the distributed database and makes the distribution transparent to users

DISTRIBUTED DBMS

TWO types of Applications

• Local application : Application that do not required data from other sites.

• Global application : Application that required data from other sites.

CONCEPTS

Characteristics DDBMS

• A collection of logically related shared data.

• Data is split into a number of fragments.

• Fragments are replicated.

•Fragments/ replicas are allocated to sites.

CONCEPTS

Characteristics Of DDBMS

• Sites are linked by a communication network.

• Data at each site is in the control of a DBMS.

•DBMS at each site can handle local applications

• Each DBMS participates in at least one global application

CONCEPTS

Properties of DDBMS

• Distributed Data Independence : Users should not have to know where data is located (extends Physical and Logical Data Independence principles).

•Distributed Transaction Atomicity : Users should be able to write Xacts accessing multiple sites just like local Xacts.

Concepts

T T T

COM 1

T T T

COM 2

Communication Network

T T T

COM 3

DB

DISTRIBUTED PROCESSING

•Reflects organizational structure

•Improved shareability and local autonomy

•Improved availability

•Improved reliability

•Improved performance

•Economics

•Modular growth

ADVANTAGES

•Complexity

•Cost

•Security

•Integrity control more difficult

•Lack of standards

•Lack of experience

•Database design more complex

DISADVANTAGES

Reference Architecture for DDBMS

Due to diversity, no accepted architecture equivalent to ANSI/SPARC 3-level architecture.

A reference architecture consists of:◦ Set of global external schemas.◦ Global conceptual schema (GCS).◦ Fragmentation schema and allocation schema.◦ Set of schemas for each local DBMS conforming to 3-level

ANSI/SPARC .Some levels may be missing, depending on

levels of transparency supported.Can be homogeneous or heterogeneous

Reference Architecture for DDBMS

• Homogeneous DDBMS

• All sites use same DBMS product.

• Heterogeneous DDBMS

• All sites use different DBMS product.

TYPE OF DDBMS

• Local DBMS

• Data Communication Component

• Global System Catalog

• Distributed DBMS component

COMPONENET ARCHITECTURE FOR DDBMS

• Fragmentation: that are used to break up the database into logical units,called fragments.

• Replication: which permits certain data to be stored in more than one site.

• Allocation: process of allocating fragments or replicas of fragments for storage at the various site.

DISTRIBUTED DATABASE DESIGN AND TECHNIQUE

• Horizontal fragment of a relation is a subset of the tuples in that relation.

• Vertical fragment of a relation keeps only certain attributes of a relation.

• Mixed – both horizontal and vertical.

• Derived – natural join first to get additional information required then fragment.

• Must be able to reconstruct original table.

• Can query and update through fragment.

TYPES OF FRAGMENTATION

FRAGMENTATION• Strategize to achieve:• Locality of Reference• Improved Reliability and Availability• Improved Performance• Balanced Storage Capacities and Costs• Minimal Communication Costs.

• Quantitative and quantitative information

• Correctness of Fragmentation• Completeness• Reconstruction• Disjointness.

REPLICATION

• Storing data at multiple sites• Example – Internet grocer with multiple

warehouses.• CUSTOMER (Cust#, Addr, Location)• Customer info at central location• Location is warehouse that makes deliveries

• Where do we store tables?• Fragment?• Replicate?

• Transparencies hide implementation details from the user

• Example in Centralized databases : Data independence

• Main types of transparencies in

• DDBMS:Distributed Transparency

• Transaction Transparency

TRANSPERENCIES IN DDBMS

Allows the user to see the database as asingle, logical entity.

If this transparency is exhibited then theuser does not need to know that 1. The data are partitioned. 2. Data can be replicated at several sites. 3. Data location.

DISTRIBUTED TRANSPARENCY

If it is provided then the user does not needto know the data is fragmented.

Example:

SELECT fName, lName FROM StaffWHERE position = ‘ Manager ’

FRAGMENTATION TRANSPERANCY

• It maintains distributed database’s integrity and consistency.

TRANSACTION TRANSPARENCY

A DBMS running across multiple processors and disks that has been designed to execute operations in parallel, whenever possible, in order to improve performance.

PARALLEL DBMS

Date’s 12 Rules for a DDBMS

Fundamental PrincipleTo the user, a distributed system should look

exactly like a non distributed system.

1. Local Autonomy2. No Reliance on a Central Site3. Continuous Operation4. Location Independence5. Fragmentation Independence6. Replication Independence

Date’s 12 Rules for a DDBMS

7. Distributed Query Processing8. Distributed Transaction Processing9. Hardware Independence10. Operating System Independence11. Network Independence12. Database Independence

Last four rules are ideals.