Summary of Database System Architectures

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Summary

• Centralized database systems run entirely on a single computer. With the growth of personal computers and local-area networking, the database front- end functionality has moved increasingly to clients, with server systems pro- viding the back-end functionality. Client – server interface protocols have helped the growth of client – server database systems.

• Servers can be either transaction servers or data servers, although the use of transaction servers greatly exceeds the use of data servers for providing database services.

Transaction servers have multiple processes, possibly running on multiple processors. So that these processes have access to common data, such as the database buffer, systems store such data in shared memory. In addition to processes that handle queries, there are system processes that carry out tasks such as lock and log management and checkpointing.

Data server systems supply raw data to clients. Such systems strive to minimize communication between clients and servers by caching data and locks at the clients. Parallel database systems use similar optimizations.

• Parallel database systems consist of multiple processors and multiple disks connected by a fast interconnection network. Speedup measures how much we can increase processing speed by increasing parallelism, for a single trans- action. Scaleup measures how well we can handle an increased number of transactions by increasing parallelism. Interference, skew, and start – up costs act as barriers to getting ideal speedup and scaleup.

• Parallel database architectures include the shared-memory, shared-disk, shared-nothing, and hierarchical architectures. These architectures have different tradeoffs of scalability versus communication speed.

• A distributed database is a collection of partially independent databases that (ideally) share a common schema, and coordinate processing of transactions that access nonlocal data. The processors communicate with one another thro- ugh a communication network that handles routing and connection strategies.

• Principally, there are two types of communication networks: local-area net- works and wide-area networks. Local-area networks connect nodes that are distributed over small geographical areas, such as a single building or a few adjacent buildings. Wide-area networks connect nodes spread over a large geographical area. The Internet is the most extensively used wide-area net- work today.

Storage-area networks are a special type of local-area network designed to provide fast interconnection between large banks of storage devices and multiple computers.

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