Difference between Pragma and Cache-Control headers?

Pragma header

• Historical Background: Primarily used in HTTP/1.0, its most common form is Pragma: no-cache.
• Function: When set to Pragma: no-cache, it instructs intermediate caching servers to validate the cache with the origin server on every request, rather than serving cached content directly.
• Limitations: The Pragma header only supports limited directives (such as no-cache) and has been superseded by the Cache-Control header in HTTP/1.1.

Cache-Control header

• Historical Background: Introduced in HTTP/1.1, it is more advanced and flexible than Pragma.
• Function: It provides multiple directives for fine-grained control over caching policies, such as no-cache, no-store, max-age, and must-revalidate, enabling developers to precisely manage caching behavior.
• Example Applications:
  • Cache-Control: no-cache: Instructs all caching systems to validate with the origin server on every request.
  • Cache-Control: max-age=3600: Specifies that the resource expires after 3600 seconds; cached content can be used directly if requested within this period.

Example Illustration

Suppose a website has a page that frequently updates content. To ensure users always see the latest content, developers can set the following HTTP headers:

• For HTTP/1.0 caching: Pragma: no-cache
• For HTTP/1.1 caching: Cache-Control: no-cache

This ensures users and caching servers access the latest page content regardless of whether they are using HTTP/1.0 or HTTP/1.1.

In summary, while both Pragma and Cache-Control can control caching, Cache-Control offers more options and greater flexibility. In environments supporting HTTP/1.1, it is recommended to use the Cache-Control header for precise caching policy control.