Parallel DBMS V.S. Distributed DBMS

　Large Scale Data Intensive Computing is a hot topic today, many people starts to talk so called Parallel Database System and Distributed Database System technologies. But these two concepts seem very confusing, so I devoted sometime to try to make it clear.

Parallel Database System seeks to improve performance through parallelization of various operations, such as data loading, index building and query evaluating. Although data may be stored in a distributed fashion in such a system, the distribution is governed solely by performance considerations.

In Distributed Database System, data is physically stored across several sites, and each site is typically managed by a DBMS capable of running independent of the other sites. In contrast to parallel databases, the distribution of data is governed by factors such as local ownership and
increased availability.

PDB & DDB Comparison:

1. System Components
- Distributed DBMS consists of many Geo-distributed, low-bandwidth link connected, autonomic sites.
- Parallel DBMS consists of tightly coupled, high-bandwidth link connected, non-autonomic nodes.

2. Component Role
- Sites in Distributed DBMS can work independently to handle local transactions or work together to handle global transactions.
- Nodes in Parallel DBMS can only work together to handle global transactions.

3. Design Purposes
= Distributed DBMS is for:
　- Sharing Data
　- Local Autonomy
　- High Availability
= Parallel DBMS is for:
　- High Performance
　- High Availability

　But both PDB&DDB need to consider the following problems: 1. Data Distribution (Placement & Replicatioin); 2. Query Parallelization(Distributed Evaluation). And also, many parallel system consists of network of workstation, the difference between Parallel DB & Distributed DB is becoming smaller.

[Reference]
1. Great Paper on PDB&DDB Explanation Distributed and Parallel Database Systems
2. Great Paper by Jim Gray Parallel Database Systems
3. Textbook, Database Management System (3rd edition)
4. Textbook, Database System Concepts (5th edition)
5. Textbook, Principle of Distributed Database Systems (2nd edition)
6. DB Textbook List @ Amazon