Home > Articles > Data > SQL Server

  • Print
  • + Share This
Like this article? We recommend

Availability Features

One of the biggest selling points that Oracle has in its arsenal is the availability features of 9i. Oracle 9i is alleged to be the most reliable, unbreakable, and scalable RDBMS on the planet, if you listen to the marketing hype.

Oracle is a very mature product, and has been offering clustering support since the mid to late '80s. Compare that with SQL Server, which has only recently offered clustering, and you can begin to see why Oracle announces its RDBMS as being the most reliable.


Some of the features discussed in this article are not available with all editions of Oracle 9i implemented on Windows 2000. You may need to purchase Oracle 9i Enterprise Edition in conjunction with Windows 2000 Advanced Server or Windows 2000 DataCenter.

Clustering Support

Clustering has been a core competency of Oracle and its products for a number of years. Oracle 9i is no exception. In fact, clustering support in Oracle's products is stronger than ever, allowing for longer uptimes and better support for ensuring that your systems are available whenever they're needed.

Unlike SQL Server, Oracle doesn't rely on Windows clustering (for Windows systems, of course), and so is not prone to the pain of setting up Windows clustering. As in SQL Server, however, there are two main types of clustering:

  • Active/active clustering. This is where an instance of Oracle actively runs on all nodes of the cluster. A passive instance of the Oracle database resides on each of the other servers in the cluster. For example, suppose that server A has database A actively serving requests to users, while server B has database B actively serving requests to users. A copy of database B resides on server A, but it doesn't actively service client requests, and vice versa for server B. Only when server A fails does the database instance failover, with that server B becoming the active server for both database A and B. This requires the hardware within the cluster to be capable of supporting multiple active instances, even if they never failover.

    Oracle has made it easier to implement active/active clustering than in the past, which can help to ensure that your site remains available whenever needed.

  • Active/passive clustering. Unlike active/active clustering, active/passive clustering means that only one node in the cluster is active at any time. For example, if server A has database A, this is the only database that it has, and it actively services requests for this database. Server B also holds a copy of database A, but doesn't service requests unless server A fails. This requires hardware to sit idle, and therefore can be very expensive to implement.

Oracle has invested heavily in clustering and is extremely advanced in this area. Their real application clusters (RAC) allow your database tier to scale out without requiring code changes to your application. The database can be integrated into the cluster, rather than having the clustering at the operating system level. This allows for superior clusters that enable the session information to be failed over with the cluster. For example, in-progress SELECT statements can be failed over so that a client's query can still be returned, even if the node it was connected to is no longer available.

Oracle recognizes the need for ensuring that when a node fails over it is recovered quickly. Unlike operating system clusters, which must restart the failover database (with a large overhead on substantial databases), Oracle clusters can ensure that both databases are instantiated even if only one database is actively servicing client requests.

Shared-Disk Servers

Oracle prides itself on the ability to scale out without causing applications to be recoded or changed significantly, to allow for extra performance provided by additional processing power.

Instead of implementing federated database servers (see Part 3 in this series), Oracle 9i incorporates shared-disk servers. This architecture differs significantly from SQL Server's federated database technology (we'll take a closer look at the differences in later articles); however, both technologies allow you to scale out your database tier.

Shared-disk clusters require that each server involved in the cluster share access to the same disk, which allows all the servers to use the same data and database schema.

To scale out the shared-disk cluster, additional hardware needs to be purchased and installed, the new instance needs to be configured, and that's it! There are no other additional tasks, as the server accesses the same disk that holds all the data and schema information as the other servers involved in the cluster.

Transaction Log Shipping

SQL Server 2000 allows transaction logs to be shipped from one server to another, thus allowing a server in another location to be created as a "warm" standby. Oracle 9i uses a similar technology to create warm standby servers. However, in Oracle terms this is referred to as a loosely coupled cluster. One database server acts as the primary server (serving requests by users), and additional servers act as standbys, generally in alternate locations. As data is updated, the main server logs are sent to the secondary servers, allowing data changes to be applied.

With the new features in 9i, DBAs can specify the amount of data delay they want between servers (15 minutes, for example). This offers the DBA the ability to ensure that accidental data changes are not replicated around the server farm too quickly. Alternatively, the DBA can specify that servers are to be kept in sync continuously, ensuring that when a DML change is committed on server A, server B sees the change almost instantaneously.


Replication is the process of copying database objects and data to other database servers within a logical network. This allows users to work on a local copy of the data; at a later time, the user's changes are replicated back to other database servers. Even if a main site fails, users will still be able to work, because they have local copies of the data available.

Oracle 9i continues its support for replication. The replication topology allows the administrator to define groups of servers as a site. These sites can then be configured to use one of the following replication scenarios:

  • Materialized views. Materialized views allow a remote site to query replicated tables and objects locally, rather than traversing the network to resolve client queries. A materialized view can be configured in one of two ways:

  • Read-only. This configuration allows a user at a remote site to perform SELECT statements and to read information in the replicated objects. When changes are registered in the replicated table, the table is totally refreshed from the master site. This configuration eliminates data conflicts.

  • Updateable. The user works on a local copy of the replicated table, and changes are pushed to and pulled from the master site. Data conflicts may occur with this configuration. An updateable materialized view configuration is generally less network-intensive than multi-master replication (described next) because only a subset of the database is replicated around the topology. It also means that client sites can contain database servers that don't require as much storage capability as the multi-master configuration.

  • Multi-master. Each site within the replication topology can make DML or DDL changes (master site), and the transactions are then replicated (pushed) around to the other sites within the topology. The way that these changes are replicated around is configurable:

  • Synchronous. Any changes made at a master site are immediately replicated to all other master sites. This option can use more network bandwidth, but may result in fewer data conflicts. If a site in the topology fails, users can query data but not perform updates (commits to the database) until the site is recovered.

  • Asynchronous. Any changes made at a site are deferred and queued to be replicated at a specified time. This is generally how replication scenarios are set up; however, while reducing network usage, it can result in more data conflicts. Even if a site goes down, users can still work, as each site is autonomous from the other sites in the topology.

  • Procedural. Reduces the need to replicate large data changes to other sites. Procedural replication tracks the stored procedure calls that modify data and issues these calls to other sites within the topology. This reduces the need to push large volumes of data around the network.

  • Hybrid configurations (multi-master and materialized). To provide a very rich replication configuration, Oracle 9i supports hybrid environments. This allows solution architects (and of course businesses) to leverage the best from both materialized and multi-master replication. For instance, an organization can create multiple master sites (multi-master) with many sub-locations (groups) that only require a subset of data from a table to work on (materialized view).

    When a change happens at the branch office, it's replicated to the closest master site, and then is replicated around the organization boundaries. This is very powerful, and gives organizations with multiple branch offices the flexibility they need without investing heavily in bandwidth.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020