1 / 15

Web Caching: Replication on the World Wide Web

Web Caching: Replication on the World Wide Web. Jonathan Bulava CSC8530 – Distributed Systems Dr. Paul Schragger. Types of Web Caches. User Agent Cache (Browser Cache) Single user Shared Cache (Proxy Cache) Multi-user Gateway Cache Multi-user. Deployment. Browser Cache.

huyen
Télécharger la présentation

Web Caching: Replication on the World Wide Web

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Web Caching:Replication on the World Wide Web Jonathan Bulava CSC8530 – Distributed Systems Dr. Paul Schragger

  2. Types of Web Caches • User Agent Cache (Browser Cache) • Single user • Shared Cache (Proxy Cache) • Multi-user • Gateway Cache • Multi-user

  3. Deployment

  4. Browser Cache • Implemented on a single user’s machine. • Local hard drive space stores representation of viewed content. • Simple rules for control. • Usefulness • Recently viewed pages (Back/Forward button) • Commonly used images

  5. Proxy Cache • Similar concept, but for multiple users. • Usually implemented on a firewall or separate device known as intermediaries. • Request routing can be manually or through an interception proxy. • Usefulness • Latency and network traffic are reduced

  6. Gateway Cache • Also known as reverse proxy caches. • Implemented on separate devices by a website administrator. • Distributed gateway caches are used in Content Delivery Networks (CDN). • Usefulness • Increased scalability, reliability, and performance

  7. 4a. Get embedded documents from local cache or server (if not already cached) 3. Get embedded documents 5. Embedded documents 4b. Embedded documents 1. Get base documents 2. Document with refs to embedded documents Content Delivery Network (CDN) Cache CDN server Client Original server Cache producer within Akamai CDN

  8. Controlling Cache • HTML Meta Tags • Written in <head> section of an HTML page. • Can mark expiration date or as uncacheable. • Only used by some browser caches and not seen by proxy caches. • HTTP Headers • Automatically created by Web server. • Sent before HTML. • Seen by browser and proxy caches.

  9. HTTP Defining Mechanisms • Freshness – Content is able to be loaded from cache without having to check with the original server. • Validation – The process of confirming with the original server whether or not cached content is still valid to load.

  10. Freshness Validation HTTP Response Headers Example HTTP/1.1 200 OK Date: Fri, 30 Oct 1998 13:19:41 GMT Server: Apache/1.3.3 (Unix) Cache-Control: max-age=3600, must-revalidate Expires: Fri, 30 Oct 1998 14:19:41 GMT Last-Modified: Mon, 29 Jun 1998 02:28:12 GMT ETag: "3e86-410-3596fbbc" Content-Length: 1040 Content-Type: text/html

  11. Expires Header and Freshness Expires: Fri, 30 Oct 1998 14:19:41 GMT • Indicates how long the representation is fresh. After this time passes, the cache will communicate with the original server to see if there have been any changes. • Beneficial for static page images as well as continually changing content. • Web server and cache must be synchronized.

  12. Cache-Control Header and Freshness Cache-Control: max-age=3600, must-revalidate • Gives control beyond Expires header. Cache control response-headers: max-age=[seconds] s-maxage=[seconds] public no-cache no-store must-revalidate proxy-revalidate

  13. Last-Modified and Validation Last-Modified: Mon, 29 Jun 1998 02:28:12 GMT • Validate cache by looking at the last time the document was altered (Last-Modified). • If-Modified-Since request is sent to the original server. If changes have been made since the date given, the entire document is returned. Otherwise, the cached document can be loaded.

  14. ETag and Validation • Unique identifiers created by server. • Changed each time the representation is altered on the original server. • If-None-Match request is sent to server and a simple comparison is used to validate the content. ETag: "3e86-410-3596fbbc"

  15. References • Nottingham, Mark. “Caching Tutorial: for Web Authors and Webmasters.” July 2006. <http://www.mnot.net/cache_docs/>. • Tanenbaum, Andrew S. Distributed Systems: Principles and Paradigms. New Jersey: Prentice-Hall, 2002. • “Web cache.” Wikipedia. <http://en.wikipedia.org/wiki/Web_cache>.

More Related