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 concurrent transactions per second while at the same
time providing subsecond response time.
Because Oracle dominates the market for Web-enabled databases, it is
the task of the Oracle manager to create a Web architecture that
satisfies these end-user requirements while at the same time
creating a flexible and scalable Web architecture.
Many of the world's top e-commerce systems use Oracle databases.
Behemoths such as
Amazon and eBay use Oracle
databases and support mindboggling transaction rates. And they make
it look easy. But the reality is that a tremendous amount of manual
effort goes into creating a Web architecture that provides a
high-performance and scalable solution for Oracle databases on the
Web.
This article explores several of the most important issues involved
in choosing a scalable Oracle Web architecture and describes some of
the choices made by successful e-commerce companies when
implementing Oracle databases over the Web.
Basic Oracle tools for an e-commerce system
Oracle has a wealth of tools that can be used to facilitate the
development of Web-based systems. These products include:
- Oracle Internet Application Server (iAS)
Oracle9i iAS is the latest incarnation of the Oracle Web
Server product. Oracle iAS claims to provide a complete framework
for the interception, routing, and management of incoming data
requests from the Internet. Oracle9i iAS competes with
freeware Web server alternatives such as Apache.
- Oracle Portal
This is the successor to the popular Web database tool that Oracle
used to facilitate the easy creation of Web pages that access
Oracle data. Oracle Portal competes with mainstream portal
products such as Plumtree
and
Digital Dashboard.
- Oracle XML
Oracle now offers a suite of XML tools to allow for the parsing of
incoming XML messages and the reformatting in sending of XML
messages. These XML interfaces facilitate communication between
portals and include utilities to parse, validate, and generate
XML.
In sum, Oracle has provided a complete suite of tools that can be
used for all phases of e-commerce development.
The Oracle product suite or a
best-of-breed solution?
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The first part of creating a Web
infrastructure is deciding whether to use the Oracle suite of
tools or to develop a custom solution with third-party tools.
Proponents of the integrated suite approach note that Oracle
will fully support all of your Web architecture. Proponents of
the best-of-breed approach argue that many of the non-Oracle
products are faster and easier.
Have you faced this choice between using all Oracle products
or selecting other products to use with Oracle? How did you
decide?
Tell us about your experiences.
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The Oracle Web architecture
Regardless of product choices, the entire e-commerce environment
must be flexible, maintainable, and scalable. 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 layer (see Figure A). Each layer
provides data caching and performs load-balancing to ensure that no
individual component is overwhelmed.
| Figure A |
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The e-commerce four-tiered architecture |
This architecture is almost infinitely scalable because additional
Web servers and application servers can be added as volume grows.
The Oracle database is also expandable, and additional Oracle
resources can be added as well. For some Oracle databases, real
application clusters can be used so that many Oracle regions can
access a single database. Here are the central components of a
four-tiered Oracle e-commerce architecture.
Web listeners
An e-commerce site must have enough listener processes so that a
single port is not overwhelmed with incoming requests. Web listeners
are simple processes that listen on a specific port and forward all
incoming requests to the least-loaded Web server. It is imperative
that the Web listeners have load-balancing intelligence so that a
single Web server is not overloaded with work.
Web servers
It is the job of the Web servers to manage the flow of the HTML and
XML. On the incoming end, the Web server validates and parses
incoming XML strings. For outbound transactions, the Web server
takes data from the application server and creates the outbound HTML
pages or XML strings. When an incoming transaction requests
services, the Web servers forward the transaction to the appropriate
application server. The Web servers also manage load and forward
requests to the least-loaded application server. Many of today's
e-commerce Web servers are custom written, borrowing heavily from
pieces of the Apache freeware code.
The Web server layer is the most challenging layer of any Oracle Web
architecture. In addition to facilitating the routing of incoming
Internet requests, the Web servers are also charged with performing
all translation formatting operations. As such, the Web server must
be able to cache as much information as possible and interface with
other ancillary tools, such as XML parsers and HTML translation
tools.
Application servers
Application servers manage all processing related to a
specific transaction. All business logic is contained at this
layer as well. Whenever a request is made to Oracle for data,
the application server funnels the request to a series of
prespawned shadow processes that hold a persistent connection
to Oracle. By preestablishing the connections between the Web
server and the Oracle database, the overhead of reestablishing
thousands of connections per second is bypassed. Most of these
systems also utilize Oracle's multithreaded server, or MTS,
which allows for the sharing of Internet memory for such
operations as sorting.
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. The Oracle database is
designed to scale to thousands of transactions per second, but
there is a significant amount of manual tuning required to
support large data volumes. This tuning involves the
resolution of disk bottlenecks, RAM memory overloads, and CPU
shortages on the database server.
Scaling the Oracle database for
e-commerce
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.
Savvy database managers do a number of things to ensure that
their Oracle database performs at optimal speeds to support
high volumes of Web traffic. To support large e-commerce
loads, many Oracle administrators implement the following
Oracle scalability features:
- Install a 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.
- Use very large RAM data buffers
Most Oracle8i and Oracle9i databases utilize very large
buffer pool storage and cache as much of the database
information as possible. The goal is to minimize disk input
and output (I/O) by having as much of the salient
information stored in RAM as possible. With Oracle's new
scalability features, it's not uncommon to see data buffers
grow anywhere from 10 GB up to 50 GB or more, effectively
caching the most important and most frequently referenced
information from the Web server. Using this approach, the
Oracle database does not need to do any unnecessary I/O, and
incoming Internet requests for information simply perform in
memory transfers from the Oracle data buffers, then go to
the Web servers, and finally back across the Internet to the
originating site.
- Presummarize aggregate information
Any Oracle e-commerce systems that are required to summarize
your aggregate information use the Oracle facility called
materialized views. With materialized views, it is possible
to precalculate aggregate information and store it in
intermediate tables, which are transparent to the Oracle
SQL. Whenever an incoming request desires an aggregation
calculation, Oracle rewrites to query the precalculated
aggregates instead of recomputing the information. This
provides the commerce system with the illusion of extremely
fast aggregation capabilities.
- Store HTML pages within the Oracle database
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 all the 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.
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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