Web server


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The inside and front of a Dell PowerEdge web server

A web server is a computer program that delivers (serves) content, such as this web page, using the Hypertext Transfer Protocol. The term web server can also refer to the computer or virtual machine running the program.
Contents
[hide]

* 1 Overview
* 2 History of web servers
* 3 Common features
* 4 Origin of returned content
* 5 Path translation
* 6 Load limits
* 7 Kernel-mode and user-mode web servers
o 7.1 Overload causes
o 7.2 Overload symptoms
o 7.3 Anti-overload techniques
* 8 Market structure
* 9 See also
* 10 References
* 11 External links

[edit] Overview

The primary function of a web server is to deliver web pages (HTML documents) and associated content (e.g. images, style sheets, JavaScripts) to clients. A client, commonly a web browser or web crawler, makes a request for a specific resource using HTTP and, if all goes well, the server responds with the content of that resource. The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting (e.g. Apache HTTP Server and PHP). This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively.

Highly niched web servers can be found in devices such as printers and routers in order to ease administration using a familiar user interface in the form of a web page.
[edit] History of web servers
The world's first web server.

In 1989 Tim Berners-Lee proposed to his employer CERN (European Organization for Nuclear Research) a new project, which had the goal of easing the exchange of information between scientists by using a hypertext system. As a result of the implementation of this project, in 1990 Berners-Lee wrote two programs:

* a browser called WorldWideWeb;
* the world's first web server, later known as CERN httpd, which ran on NeXTSTEP.

Between 1991 and 1994 the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among lots of different social groups of people, first in scientific organizations, then in universities and finally in industry.

In 1994 Tim Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved (HTTP, HTML, etc.) through a standardization process.
[edit] Common features

1. Virtual hosting to serve many web sites using one IP address.
2. Large file support to be able to serve files whose size is greater than 2 GB on 32 bit OS.
3. Bandwidth throttling to limit the speed of responses in order to not saturate the network and to be able to serve more clients.

[edit] Origin of returned content

The origin of the content sent by server is known as:

* static if it comes from an existing file lying on a file system;
* dynamic if it is dynamically generated by some other program or script or application programming interface (API) called by the web server.

Serving static content is usually much faster (from 2 to 100 times) than serving dynamic content, especially if the latter involves data pulled from a database.
[edit] Path translation

Web servers are able to map the path component of a Uniform Resource Locator (URL) into:

* a local file system resource (for static requests);
* an internal or external program name (for dynamic requests).

For a static request the URL path specified by the client is relative to the Web server's root directory.

Consider the following URL as it would be requested by a client:

http://www.example.com/path/file.html

The client's web browser will translate it into a connection to www.example.com with the following HTTP 1.1 request:

GET /path/file.html HTTP/1.1
Host: www.example.com

The web server on www.example.com will append the given path to the path of its root directory. On Unix machines, this is commonly /var/www. The result is the local file system resource:

/var/www/path/file.html

The web server will then read the file, if it exists, and send a response to the client's web browser. The response will describe the content of the file and contain the file itself.
[edit] Load limits

A web server (program) has defined load limits, because it can handle only a limited number of concurrent client connections (usually between 2 and 80,000, by default between 500 and 1,000) per IP address (and TCP port) and it can serve only a certain maximum number of requests per second depending on:

* its own settings;
* the HTTP request type;
* content origin (static or dynamic);
* the fact that the served content is or is not cached;
* the hardware and software limits of the OS where it is working.

When a web server is near to or over its limits, it becomes overloaded and thus unresponsive.
[edit] Kernel-mode and user-mode web servers

A web server can be either implemented into the OS kernel, or in user space (like other regular applications).

An in-kernel web server (like TUX on Linux or Microsoft IIS on Windows) will usually work faster because, as part of the system, it can directly use all the hardware resources it needs, such as:

* non-paged memory;
* CPU time-slices;
* network adapters buffers.

Web servers that run in user-mode have to ask the system the permission to use more memory or more CPU resources. Not only these requests to the kernel take time, but they are not always satisfied because the system reserves resources for its own usage and has the responsibility to share hardware resources with all the other running applications.

Also applications cannot access the system internal buffers, which is causing useless buffer copies that create another handicap for user-mode web servers. As a consequence, the only way for a user-mode web server to match kernel-mode performances is to raise the quality of its code to much higher standards than the code used into another web server that runs in the kernel.

This is more difficult under Windows than under Linux where the user-mode overhead is 6 times smaller than under Windows.[1]
[edit] Overload causes

At any time web servers can be overloaded because of:

* Too much legitimate web traffic. Thousands or even millions of clients hitting the web site in a short interval of time. (e.g. Slashdot effect);
* DDoS. Distributed Denial of Service attacks;
* Computer worms that sometimes cause abnormal traffic because of millions of infected computers (not coordinated among them);
* XSS viruses can cause high traffic because of millions of infected browsers and/or web servers;
* Internet web robots. Traffic not filtered/limited on large web sites with very few resources (bandwidth, etc.);
* Internet (network) slowdowns, so that client requests are served more slowly and the number of connections increases so much that server limits are reached;
* Web servers (computers) partial unavailability. This can happen because of required or urgent maintenance or upgrade, hardware or software failures, back-end (e.g. DB) failures, etc.; in these cases the remaining web servers get too much traffic and become overloaded.

[edit] Overload symptoms

The symptoms of an overloaded web server are:

* requests are served with (possibly long) delays (from 1 second to a few hundred seconds);
* 500, 502, 503, 504 HTTP errors are returned to clients (sometimes also unrelated 404 error or even 408 error may be returned);
* TCP connections are refused or reset (interrupted) before any content is sent to clients;
* in very rare cases, only partial contents are sent (but this behavior may well be considered a bug, even if it usually depends on unavailable system resources).

[edit] Anti-overload techniques

To partially overcome above load limits and to prevent overload, most popular web sites use common techniques like:

* managing network traffic, by using:
o Firewalls to block unwanted traffic coming from bad IP sources or having bad patterns;
o HTTP traffic managers to drop, redirect or rewrite requests having bad HTTP patterns;
o Bandwidth management and traffic shaping, in order to smooth down peaks in network usage;
* deploying web cache techniques;
* using different domain names to serve different (static and dynamic) content by separate Web servers, i.e.:
o

http://images.example.com

o

http://www.example.com

* using different domain names and/or computers to separate big files from small and medium sized files; the idea is to be able to fully cache small and medium sized files and to efficiently serve big or huge (over 10 - 1000 MB) files by using different settings;
* using many Web servers (programs) per computer, each one bound to its own network card and IP address;
* using many Web servers (computers) that are grouped together so that they act or are seen as one big Web server, see also: Load balancer;
* adding more hardware resources (i.e. RAM, disks) to each computer;
* tuning OS parameters for hardware capabilities and usage;
* using more efficient computer programs for web servers, etc.;
* using other workarounds, especially if dynamic content is involved.

[edit] Market structure
Market share of major web servers
For more details on HTTP server programs, see Category:Web server software.

Given below is a list of top Web server software vendors published in a Netcraft survey in January 2009.
Vendor Product Web Sites Hosted Percent
Apache Apache 108,078,535 46.90%
Microsoft IIS 49,723,999 21.58%
Tencent qq.com 30,069,136 13.05%
Google GWS 13,819,947 6.0%
nginx nginx 13,813,997 5.99%
lighttpd lighttpd ???? ??.??%
[edit] See also

* Application server
* Comparison of web server software
* Comparison of lightweight web servers
* HTTP compression
* Open source web application
* SSI, CGI, SCGI, FastCGI, PHP, Java Servlet, JavaServer Pages, ASP, ASP .NET, Server API
* Virtual hosting
* Web hosting service
* Web service

[edit] References

1. ^ High performance kernel mode web server for Windows

[edit] External links

* World Web Server Usage Statistics
* RFC 2616, the Request for Comments document that defines the HTTP 1.1 protocol.
* C64WEB.COM - Commodore 64 running as a webserver using Contiki

[hide]
v • d • e
Website management
Concepts
Drop registrar · Overselling · Web document · Web content · Web hosting service · Web server · Webmaster
Web hosting tools
Comparison of control panels · cPanel · DirectAdmin · Domain Technologie Control · ehcp · H-Sphere · InterWorx · ISPConfig · ispCP · LxAdmin · Plesk · Usermin · Webmin
Domain name managers and registrars
AusRegistry · CZ.NIC · CIRA · CNNIC · DENIC · DNS Belgium · Domainz · ENom · Go Daddy · Melbourne IT · Museum Domain Management Association · Name.com · Network Solutions · NeuStar · OLM.net · Register.com · Tucows · Web.com
Web content management system
Conference management system · Document management system · Wiki software · Weblog software
Retrieved from "http://en.wikipedia.org/wiki/Web_server"
Categories: Servers | Web server software | Website management | Web development

MESIN PENCARI



Mesin pencari adalah program komputer yang dirancang untuk membantu seseorang menemukan file-file yang disimpan dalam komputer, misalnya dalam sebuah server umum di web (WWW) atau dalam komputer sendiri. Mesin pencari memungkinkan kita untuk meminta content media dengan kriteria yang spesifik (biasanya yang berisi kata atau frasa yang kita tentukan) dan memperoleh daftar file yang memenuhi kriteria tersebut. Mesin pencari biasanya menggunakan indeks (yang sudah dibuat sebelumnya dan dimutakhirkan secara teratur) untuk mencari file setelah pengguna memasukkan kriteria pencarian.

Dalam konteks Internet, mesin pencari biasanya merujuk kepada WWW dan bukan protokol ataupun area lainnya. Selain itu, mesin pencari mengumpulkan data yang tersedia di newsgroup, database besar, atau direktori terbuka seperti DMOZ.org. Karena pengumpulan datanya dilakukan secara otomatis, mesin pencari berbeda dengan direktori Web yang dikerjakan manusia.

Sebagian besar mesin pencari dijalankan oleh perusahaan swasta yang menggunakan algoritma kepemilikan dan database tertutup - yang paling populer adalah Google (MSN Search dan Yahoo! tertinggal sedikit di belakang). Telah ada beberapa upaya menciptakan mesin pencari dengan sumber-terbuka (open-source), contohnya adalah Htdig, Nutch, Egothor dan OpenFTS.
Daftar isi

* 1 Cara kerja mesin pencari
* 2 Beberapa Tips Mencari dengan Menggunakan Mesin Pencari
* 3 Sejarah
o 3.1 Google
* 4 Tantangan yang dihadapi mesin-mesin pencari
* 5 Lihat pula
* 6 Pranala luar
o 6.1 Pranala menuju mesin pencari
o 6.2 Engine MetaSearch



Google

Sekitar tahun 2001, mesin pencari Google berkembang lebih besar. Keberhasilan ini didasarkan pada bagian konsep dasar dari link popularity dan PageRank. Setiap halaman diurutkan berdasarkan seberapa banyak situs yang terkait, dari sebuah premis bahwa situs yang diinginkan pasti lebih banyak terkoneksi daripada yang lain. Rangking situs (The PageRank)dari sebuah link halaman dan jumlah link dari halaman-halaman tersebut merupakan masukan bagi Rangking situs yang bersangkutan. Hal ini memungkinkan bagi Google untuk mengurutkan hasilnya berdasarkan seberapa banyak halaman situs yang menuju ke halaman yang ditemukannya. User interface Google sangat disukai oleh pengguna, dan hal ini berkembang ke para pesaingnya.

Researchers at NEC Research Institute claim to have improved upon Google's patented PageRank technology by using web crawlers to find "communities" of websites. Instead of ranking pages, this technology uses an algorithm that follows links on a webpage to find other pages that link back to the first one and so on from page to page. The algorithm "remembers" where it has been and indexes the number of cross-links and relates these into groupings. In this way virtual communities of webpages are found. Sejarah

Mesin pencari pertama adalah "Wandex", yang sekarang index yang tidak berfungsi dari World Wide Web Wanderer, suatu web crawler dibangun oleh Matthew Gray di MIT pada 1993. Mesin pencari lain yang lama, Aliweb, juga muncul di 1993 dan masih berjalan hingga saat ini. Salah satu mesin pencari pertama yang sekarang berkembang menjadi usaha komersial yang cukup besar adalah Lycos, yang dimulai di Carnegie Mellon University sebagai proyek riset di tahun 1994.

Segera sesudah itu, banyak mesin pencari yang bermunculan dan bersaing memperebutkan popularitas. Termasuk di antaranya adalah WebCrawler, Hotbot, Excite, Infoseek, Inktomi, dan AltaVista. Mereka bersaing dengan direktori-direktori populer seperti misalnya Yahoo. Belakangan direktori-direktori ini menggabungkan atau menambahkan teknologi mesin pencari agar fungsinya semakin meningkat.

Pada tahun 2002, Yahoo! mengakuisisi Inktomi dan pada 2003, mengakuisisi Overture yang memiliki AlltheWeb dan Altavista. Tahun 2004, Yahoo! meluncurkan mesin pencarinya sndiri yang didasarkan pada teknologi gabungan dari mesin-mesin yang telah diakuisisinya dan memberikan pelayanan yang mengutamakan mesin pencari Web daripada direktorinya.

Pada Desember 2003, Orase menerbitkan versi pertama dari teknologi pencari waktu-riilnya. Mesin ini memiliki banyak fungsi baru dan performancenya meningkat sangat hebat.

Mesin pencari juga dikenal sebagai bintang-bintang yang paling cemerlang dalam perlombaan investasi Internet yang terjadi pada akhir tahun 1990-an. Beberapa perusahaan masuk ke dalam pasar dengan hebat, mencatat keuntungan besar pada penawaran publik pertamanya. Sebagian lagi sama sekali menyingkirkan mesin pencari publiknya, dan hanya memasarkan edisi-edisi Enterprise saja, seperti misalnya Northern Light yang dulunya adalah salah satu dari 8 atau 9 mesin pencari awal setelah Lycos muncul.

Sebelum munculnya Web, ada pula mesin-mesin pencari untuk [protokol]] atau penggunaan lain, seperti misalnya Archie search engine untuk situs-situs FTP anonim dan Veronica search engine untuk Gopher protocol.

Buku Osmar R. Zaïane From Resource Discovery to Knowledge Discovery on the Internet menjelaskan secara rinci sejarah teknologi mesin pencari sebelum munculnya Google.

Mesin-mesin pencari lainnya mencakup a9.com, AlltheWeb, Ask Jeeves, Clusty, Gigablast, Teoma, Wisenut, GoHook, Kartoo, dan Vivisimo. Cara kerja mesin pencari

Mesin pencari web bekerja dengan cara menyimpan informasi tentang banyak halaman web, yang diambil langsung dari WWW. Halaman-halaman ini diambil dengan web crawler — browser web otomatis yang mengikuti setiap pranala yang dilihatnya. Isi setiap halaman lalu dianalisis untuk menentukan cara mengindeksnya (misalnya, kata-kata diambil dari judul, subjudul, atau field khusus yang disebut meta tag). Data tentang halaman web disimpan dalam sebuah database indeks untuk digunakan dalam pencarian selanjutnya. Sebagian mesin pencari, seperti Google, menyimpan seluruh atau sebagian halaman sumber (yang disebut cache) maupun informasi tentang halaman web itu sendiri.

Ketika seorang pengguna mengunjungi mesin pencari dan memasukkan query, biasanya dengan memasukkan kata kunci, mesin mencari indeks dan memberikan daftar halaman web yang paling sesuai dengan kriterianya, biasanya disertai ringkasan singkat mengenai judul dokumen dan terkadang sebagian teksnya.

Ada jenis mesin pencari lain: mesin pencari real-time, seperti Orase. Mesin seperti ini tidak menggunakan indeks. Informasi yang diperlukan mesin tersebut hanya dikumpulkan jika ada pencarian baru. Jika dibandingkan dengan sistem berbasis indeks yang digunakan mesin-mesin seperti Google, sistem real-time ini unggul dalam beberapa hal: informasi selalu mutakhir, (hampir) tak ada pranala mati, dan lebih sedikit sumberdaya sistem yang diperlukan. (Google menggunakan hampir 100.000 komputer, Orase hanya satu.) Tetapi, ada juga kelemahannya: pencarian lebih lama rampungnya.

Manfaat mesin pencari bergantung pada relevansi hasil-hasil yang diberikannya. Meskipun mungkin ada jutaan halaman web yang mengandung suatu kata atau frase, sebagian halaman mungkin lebih relevan, populer, atau autoritatif daripada yang lain. Kebanyakan mesin pencari menggunakan berbagai metode untuk menentukan peringkat hasil pencarian agar mampu memberikan hasil "terbaik" lebih dahulu. Cara mesin menentukan halaman mana yang paling sesuai, dan urutan halaman-halaman itu diperlihatkan, sangat bervariasi. Metode-metodenya juga berubah seiring waktu dengan berubahnya penggunaan internet dan berevolusinya teknik-teknik baru.

Sebagian besar mesin pencari web adalah usaha komersial yang didukung pemasukan iklan dan karenanya sebagian menjalankan praktik kontroversial, yaitu membolehkan pengiklan membayar agar halaman mereka diberi peringkat lebih tinggi dalam hasil pencarian.