Basic Caching Terminology

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Basic Caching Terminology
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Table of Contents

• Caching
• Websites
• Web Caching
• Benefits of Web Caching
• Caching Terminology
• Origin Server

• Cache Hit Ratio
• Freshness
• Stale Content
• Validation
• Invalidation

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Caching

• Caching refers to the process of storing files
  copies in a cache, which is a temporary storage
  location, for the purpose of making these quickly
  accessible.
• In the context of websites, their HTML files,
  images and JavaScript are cached by web browsers
  for loading websites swiftly. Examples of other
  types of caching include DNS (Domain Name System)
  servers that cache DNS records to ensure faster
  lookups and CDN (Content Delivery Network)
  servers that cache content to achieve reduced
  latency.

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Websites

• YELLOW
• Prior to delving into web caching and the terms
  that are most commonly used in it, it is
  important to understand briefly about websites
  and how these are made accessible.
• A website, which can be identified by a common
  domain name, is a collection of related web pages
  and content. It is located under a single domain
  name. All the websites that can be accessed
  publicly over the Internet, collectively form the
  World Wide Web (www). A websites content
  usually focusses on a specific topic or purpose.
• Every websites files are stored on and delivered
  from a web server. Web servers are made available
  through the service of web hosting, which can be
  of many types, and is provided by web hosting
  companies. The most efficient web hosting
  companies usually get referred to as the Best
  Windows Hosting Company or as the Best
  WordPress Hosting in 2021 or as the Top Cloud
  Hosting Company.

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Web Caching

• Web caching is the process of temporarily storing
  Web documents that include Web pages and various
  types of Web multimedia in order to decrease
  server lag. Copies of documents that pass through
  a Web cache system, which can be an appliance or
  a computer program, are stored by it. In the
  event that certain conditions are met, subsequent
  requests may be fulfilled from the cache. This
  helps to prevent the origin server from getting
  overloaded.
• Web caching increases page delivery speed
  substantially along with reducing the work of the
  backend server. Moreover, it assures protection
  against total outages. It can deliver content
  that had been cached, in the event that servers
  are down.

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Benefits of Web Caching

• YELLOW
• Both, content providers and content consumers,
  reap the benefits of web caching. Its major
  benefits with regard to content delivery are
  mentioned below.
• Enhanced responsiveness
• Content availability despite network
  interruptions
• Reduced network costs
• Enhanced performance with the same hardware

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Caching Terminology
Caching might usually involve such terms that
might be unfamiliar to many. Some of the most
common terms that get used in caching are origin
server, cache hit ratio, freshness, stale
content, validation and invalidation. More
detailed information will be provided on these
terms in the following slides.
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Origin Server

• YELLOW
• The original location of the Web content is the
  origin server. It is controlled by the Web server
  administrator. It processes as well as responds
  to Internet clients incoming Internet requests.
  Moreover, it sets all the contents caching
  policy. The physical distance that exists between
  an origin server and the client that makes a
  request, results in the connections latency.
  This leads to an increase in the time that is
  required by a webpage to be loaded.

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Cache Hit
Ratio

• YELLOW
• A cache hit ratio, which is usually referred to
  as the hit rate, measures a caches
  effectiveness. This is a ratio of the number of
  requests that can be retrieved from a cache to
  the total number of requests that are made. The
  higher the cache hit ratio, the higher the
  percentage of the content that has been retrieved
  from the cache.

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Freshness

• YELLOW
• Freshness denotes whether an item that is within
  a cache can still be considered for serving to a
  specific client. If the content in a cache is
  within the time frame that equates to freshness,
  as per the caching policy, then it will be used
  to respond.

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Stale Content

• YELLOW
• Stale content refers to expired content, which
  cannot be used for responding to client request.
  The cache freshness settings that depend on the
  caching policy determine the expiration of items
  in the cache. New content can be retrieved by
  recontacting the origin server.

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Validation

• YELLOW
• Validation refers to the process of ascertaining
  with the origin server if the cached content
  represents the latest version of the item. The
  stale items that exist in the cache can be
  validated for the purpose of refreshing their
  expiration time.

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Invalidation

• YELLOW
• When content is removed from the cache prior to
  its specified expiration date, this process is
  known as invalidation. This is required in the
  event that an item changes on the origin server
  and the presence of such an outdated item in the
  cache can result in problems for the client.

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