Duties of a database

Integrity

Integrity means that the database, or the programs that create its content, embody means of preventing users who provide data from breaking the system’s business rules. For example, a retailer may have a business rule that only individual customers can place orders; and so every order must identify one and only one customer. Oracle Server and other relational DBMSs enforce this type of business rule with constraints, which are configurable implicit queries. To continue the example, in the process of inserting a new order the database may query its customer table to make sure that the customer identified by the order exists.

Security and Availability

Security means that users’ ability to access and change data conforms to the policies of the business and the delegation decisions of its managers. Like other metadata, a relational DBMS manages security information in the form of tables. These tables are the “keys to the kingdom� and so it is important to protect them from intruders.

Availability means that authorized users can access and change data as needed to support the business. Increasingly, businesses are coming to expect their data to be available at all times (“24x7�, or 24 hours a day, 7 days a week, ). The IT industry has responded to the availability challenge with hardware and network redundancy and increasing online administrative capabilities.

Performance

Performance means that the database does not cause unreasonable online response times, and it does not cause unattended programs to run for an unworkable period of time. In complex client/server and three-tier systems, the database is just one of many elements that determine the performance that online users and unattended programs experience. Performance is a major motivation for the DBA to become a generalist and coordinate with specialists in other parts of the system outside of traditional bureaucratic reporting lines.

Techniques for database performance tuning have changed as DBA's have become more sophisticated in their understanding of what causes performance problems and their ability to diagnose the problem.

In the 1990s, DBAs often focused on the database as a whole, and looked at database-wide statistics for clues that might help them find out why the system was slow. Also, the actions DBAs took in their attempts to solve performance problems were often at the global, database level, such as changing the amount of computer memory available to the database, or changing the amount of memory available to any database program that needed to sort data.

Around the year 2000, many of the most fundamental assumptions about database performance tuning were discovered to be myths. Most famously, the database buffer cache hit ratio, once thought to be the most reliable way to measure database performance, was found to be a completely meaningless statistic.

As of 2005, the fog has lifted. DBA's understand that performance problems initially must be diagnosed, and this is best done by examining individual SQL programs, not the database as a whole. Various tools, some included with the database and some available from third parties, provide a behind the scenes look at how the database is handling the SQL program, shedding light on what's taking so long.

Having identified the problem, the individual SQL statement can be tuned, and this is usually done by either rewriting it, using hints, adding or modifying indexes, or sometimes modifying the database tables themselves.

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