Software Engineering for Internet Applications - Student Community

Chapter 11Scaling GracefullyLet's look again at Christopher Alexander's words from A PatternLanguage, quoted in the "Planning" chapter:"It is not hard to see why the government of a region becomes lessand less manageable with size. In a population of N persons, thereare of the order of N^2 person-to-person links needed to keepchannels of communication open. Naturally, when N goes beyond acertain limit, the channels of communication needed for democracyand justice and information are simply too clogged, and too complex;bureaucracy overwhelms human process. ..."We believe the limits are reached when the population of a regionreaches some 2 to 10 million. Beyond this size, people becomeremote from the large-scale processes of government. Our estimatemay seem extraordinary in the light of modern history: the nationstateshave grown mightily and their governments hold power overtens of millions, sometimes hundreds of millions, of people. But thesehuge powers cannot claim to have a natural size. They cannot claimto have struck the balance between the needs of towns andcommunities, and the needs of the world community as a whole.Indeed, their tendency has been to override local needs and represslocal culture, and at the same time aggrandize themselves to thepoint where they are out of reach, their power barely conceivable tothe average citizen."Let's also remind ourselves of the empirical evidence that enormousonline communities cannot satisfy every need. America Online hasnot subsumed all the smaller communities on the Internet. Peopleunsubscribe from mailing lists when the traffic level becomes toohigh. Early adopters of USENET discussion groups ("Netnews")stopped participating because they found the utility of the groupsdiminishing when the community size grew beyond a certain point.So the good news is that, no matter how large one's competitors,there will always be room for a new online community. The bad newsis that growth results in significant engineering challenges. Some ofthe challenges boil down to simple performance engineering: Howcan one divide the load of supporting an Internet application amongmultiple CPUs and disk drives? These can typically be solved withmoney, even in the absence of any cleverness. The deeperFor example, if you place the following inc:\Inetpub\wwwroot\Web.config (assuming default IISinstallation)you will be able to access publisherEmail in a VB .aspx page asfollows...For further information please contact us at ...By default, configuration settings apply to a directory and all itssubdirectories. Also by default, these settings can be overridden bysettings in Web.config files in the subdirectories. More elaboraterules for scoping and override behavior can be established using thetag.More:• http://msdn.microsoft.com/library/default.asp?url=/library/enus/cpguide/html/cpconaspnetconfiguration.asp(note that theMSDN guys haven't figured out how to do abstract URLsand they also haven't converted to .aspx yet!)200149