Author: Donald Burleson

Today's Web development managers are more challenged than ever to find the appropriate tools and technologies for their mission-critical Oracle databases. With the explosive interest in e-commerce, end users have high expectations. They demand systems on the Web that can support thousands of simultaneous transactions per second while at the same time providing efficient response time.

Oracle Web-enabled databases:

Because Oracle dominates the market for web-enabled databases; it is the task of the Oracle manager to:

• Create a web architecture that satisfies the end-user requirements.
• Create flexible and scalable web architecture.

Oracle Databases: Four-Tiered Architecture - Benefits:

Many of the top e-commerce companies are choosing a four-tiered architecture to support their Oracle databases.

• The four-tiered architecture isolates processing requirements at each level and provides independence for each.
• Each layer provides data caching and performs load-balancing to ensure that no individual component is overwhelmed.
• The four-tiered architecture is almost infinitely scalable because additional Web servers and application servers can be added as volume grows.
• The Oracle database is expandable.
• Oracle resources can be added.
• For some Oracle databases, real application clusters can be used so that many Oracle regions can access a single database

Oracle Databases: Four-Tiered Architecture - Components:

Here are the central components of a four-tiered Oracle e-commerce architecture.

• Web listeners: Web listeners are simple processes that listen on a specific port and forward all incoming requests to the least-loaded Web server.
• Web servers: In addition to facilitating the routing of incoming Internet requests, the Web servers are also charged with performing all translation formatting operations.
• Application servers: Application servers manage all processing related to a specific transaction. All business logic is contained at this layer as well.
• Database server: At the Oracle database layer, the Oracle relational database management system (RDBMS) must be able to support all incoming requests from the application servers.

Scalable Oracle database – How?

Now that we've discussed the functions of each layer in the four-tiered architecture, let's take a closer look at managing Oracle in a Web environment. To support large e-commerce loads, many Oracle administrators implement the following Oracle scalability features:

Multithreaded server:

By using a multithreaded server

• The Oracle database can utilize internal memory within the Oracle region called a large pool.
• The multithreaded server also allows for many thousands of end users to connect through response dispatchers. Each dispatcher within the Oracle database can spawn many subtasks to handle high volumes of incoming connections. 

Buffer Pool Storage and Cache:

Most Oracle8i and Oracle9i databases utilize very large buffer pool storage and cache as much of the database information as possible. The large RAM data buffers minimizes disk input and output (I/O) by having as much of the salient information stored in RAM as possible.

Materialized Views:

Materialized views make it possible to pre-calculate aggregate information and store it in intermediate tables. The intermediate tables are transparent to the Oracle SQL. Whenever an incoming request desires an aggregation calculation, Oracle rewrites to query the pre-calculated aggregates instead of recomputing the information. This provides extremely fast aggregation capabilities.  

Character large objects (CLOBS):

Many high-volume Oracle e-commerce systems choose to store preformatted HTML text in one of Oracle's numerous data types that support large objects. These data types include character large objects (CLOBS). Oracle takes these large objects and stores them either offline within the Oracle data files or offline using file linkages. By using this technique, the Web server is relieved of the tedious chore of having to redefine the entire outgoing HTML upon a request from the end user. The preformatted HTML makes its way from the Oracle data buffers to the Web server cache, where all variables are parameterized. When incoming data requests a specific HTML page, symbolic substitution takes place within the cached version of the HTML page on the Web server, and a complete HTML page (with the Oracle data embedded into the HTML) is shipped back across the Internet.

Final Thoughts:

Of course, it's impossible for one article to fully cover all of the area of Oracle management for Web systems. But this overview has introduced several important architectural considerations for constructing a robust Oracle system over the Web. It is only with proper management and planning that your Oracle database will be able to scale to large data volumes while remaining flexible.

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