CODEWITHSUNDEEP
cachinghttp-caching
99miles
99miles

Reputation: 11212

Setting both Expires and Cache-Control: max-age

Can someone clarify this statement about caching.

https://developers.google.com/speed/docs/best-practices/caching says

It is redundant to specify both Expires and Cache-Control: max-age, or to specify both Last-Modified and ETag.

Then later it says

The fingerprinting mechanism allows the server to set the Expires header to exactly one year ahead of the request date; the Last-Modified header to the date the file was last modified; and the Cache-Control: max-age header to 3153600.

This latter statement goes against the prior -- about not setting both the Expires and Cache-Control.

Is the first statement the norm, and the second an exception? Or is this doc simply going against it's own recommendations? What's suggested?

Thanks.

Upvotes: 5

Views: 5570

Answers (2)

Milos Gavrilov
Milos Gavrilov

Reputation: 436

[Cache-Control:max-age] and [Expires] in Http are doing the same thing and that is a reason why they are redundant. But there are still some big differences between them, [Cache-Control] is http/1.1 standard and Expires is http/1.0. If client browser does not support http/1.1 Cache-Control will be ignored, and that is a reason why you can use them both.

If you use them both, [Cache-Control] has priority. More information you can find here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.3

Upvotes: 13

Igal Zeifman
Igal Zeifman

Reputation: 1146

Well...

I can tell you that the first statement is correct, because you really don't need to specify both [Expires] and [Max-Age] headers since they both do the same thing (setting max period for Caching)

Same also goes for [Last Modify] and [Etag], as both address freshness.

I agree that there seems to be some confusion, as the example they give later on uses both [Expires] and [Max-Age] headers.

At first glance this looks like some kind of documentation error.

Still, You need to remember that , while you don't have to use both [Expires] and [Max-Age], you surely can use them both, just as long as they point to the same date - like in the example they provide.

To summarize:

The first statement talks about redundancy (which is not necessary "bad", and can be "just" wasteful). The example they give later on, while not optimized, will cause no issues.

As long as you don't set different expiration dates using the two headers, you`ll be just fine.

Upvotes: 2

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