Strong Caching and Conditional Caching

Strong Caching and Conditional Caching

Strong Caching

Definition: Strong caching refers to the browser's ability to fetch resources directly from the local cache without any interaction with the server during the cache validity period.

Characteristics:

• Cache Control Headers:
  • Cache-Control: max-age=<seconds>: Specifies the maximum duration (in seconds) the resource can be cached.
  • Expires: <date>: Specifies the expiration date and time for the resource.
• Behavior:
  • No Server Interaction: During the cache validity period, the browser retrieves the resource from the local cache without contacting the server.
  • Improved Performance: Significantly improves performance since no server requests are made.
• Suitable For: Static resources that do not change frequently, such as images, CSS files, and JavaScript files.

Example Response Headers:

HTTP/1.1 200 OK
Cache-Control: max-age=3600
Expires: Wed, 21 Oct 2025 07:28:00 GMT
Content-Type: application/json

{ "id": 1, "name": "John Doe" }

Conditional Caching

Definition: Conditional caching, also known as negotiated caching, involves the browser sending requests to the server to validate cached resources. The server determines whether the cached resource is still valid.

Characteristics:

• Cache Control Headers:
  • ETag: A unique identifier for the resource.
  • Last-Modified: The date and time when the resource was last modified.
• Request Headers:
  • If-None-Match: Sent by the browser, containing the ETag value to validate the resource.
  • If-Modified-Since: Sent by the browser, containing the last modified date to validate the resource.
• Behavior:
  • Server Interaction: Each request involves server interaction to validate the resource.
  • Freshness Check: If the resource has not changed, the server responds with 304 Not Modified, allowing the browser to use the cached version.
  • Performance: Slightly lower performance compared to strong caching due to server validation.
• Suitable For: Resources that change frequently but still need to be cached.

Example Request and Response Headers: First Request Response:

HTTP/1.1 200 OK
ETag: "abc123"
Last-Modified: Tue, 20 Apr 2023 07:28:00 GMT
Content-Type: application/json

{ "id": 1, "name": "John Doe" }

Subsequent Request:

GET /resource HTTP/1.1
Host: example.com
If-None-Match: "abc123"
If-Modified-Since: Tue, 20 Apr 2023 07:28:00 GMT

Server Response:

HTTP/1.1 304 Not Modified