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Advantages And Disadvantages Of DDBMS

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Contents:
1. Classification of DDBMS
2. Distributed Database Architecture

Introduction
Distributed database brings the advantages of distributed computing to the database management domain. A distributed computing system consists of the number of processing elements that are connected in the computer network which performing certain tasks.
Classification of DDBMS:
1. Distributed Fragmentation and Replication
2. Degree of homogeneity/Heterogeneity
3. Degree of autonomy
4. Degree of Distribution transparencies
5. DDBMS query processing and optimization
6. DDBMS concurrent control
7. DDBMS Transaction processing

Distributed Database Architecture
• Database is distributed at the DBMS
• In a distributed database system (DDS), multiple Database Management Systems run on multiple servers (sites or nodes) …show more content…

• This copy of the data item is where all locks are applied. The concurrency controller should look to this copy to determine if any locks are held.
• Several variations of distinguished copy:
1. All distinguished copies reside on the same node: Primary Site
2. Distinguished copies may reside on different sites: Primary Copy
• There are problems with this approach: o What if the primary site fails or if the node where the primary copy resides fails? o One solution is to designate a backup site that will automatically take over. o Another solution is to "elect" a new primary site/copy.
• Another overall approach (aside from distinguished copy), is to use a Voting protocol: To lock a data item:
0. Send a message to all nodes that maintain a replica of this item.
1. If a node can safely lock the item, then vote "Yes", otherwise, vote "No".
2. If a majority of participating nodes vote "Yes" then the lock is granted.
3. Send the results of the vote back out to all participating sites.
• With the voting approach, nodes can fail and recover while allowing transaction processing to

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