How should I configure If-Modified-Since on database-driven pages?

[nickstout513]

This is a "tasteful" video. =p

[olbywong717c]

This video went viral on Albania 

[tamekawelle]

great clip .. keep it up thanks

[SebastianXgib]

For a comprehensive tutorial with ready-to-use PHP code lookup Sebastian's Pamphlets, or query Google for [Save bandwidth costs: Dynamic pages can support If-Modified-Since too].

[NoirNG]

@kron3r Nonono... the header your server is sending is Last-Modified. The request made by the client may be conditional: if the request contains the If-Modified-Since header AND the modification timestamps are equal (= no modification, since client has the current version), your server should respond with "304 Not Modified" and NOT send the body.

If the condition is not met (= your server has different timestamp), the body is transferred as if no conditional request was made.

[kron3r]

Yeah, what @NoirNG said.

[kisvarosipari]

how can we know wether or not our web page has if-modified-since so that we update it or it has not so that we let the google crawl it without changing it.

[NoirNG]

@kisvarosipari web-sniffer (DOT) net - Look for the Last-Modified header in the response. If it exists, click on the date. If it shows 304 Not Modified, then everything works perfectly.

[NoirNG]

An important tip for webmasters: if you do want caches down the line to revalidate the content they have with that of the origin servers on every request, you should set the Last-Modified but _not_ the Expires header. Also, you should send max-age=0 in the Cache-Control header. For some strange reason, Squid sometimes ignores the must-revalidate and proxy-revalidate attributes. By using my tip, you can benefit from caching but also provide 100% fresh content the entire time.

[lillmii3o]

Thanks for your wonderful answers in all videos. Really appriciated!

[tattoos01]

I'm guessing the Last modification date in an xml sitemap does the same thing.

So if you cannot update the header info as the database changes, maybe updating the "Last modification date" of your sitemap will get Google to re crawl.

But that raises another question, does one overrides the other? If so, which one does Google favor?

Cheers

James

[NoirNG]

@tattoos01 The sitemap's lastmod attribute doesn't have anything to do with the Last-Modified header your server should be sending. Implementing 304 Not Modified is crucial if you want to save bandwidth.

[theylmdl]

Actually, "If-Modified-Since" ist part of the client's request header and the server's response should be in the "Last-Modified" key.

[chrisybwell]

Toe mo?

I think it is pronounced Tom oh.

[genmodo]

First

[ordiantakeover]

@genmodo Good for you.

Thank you Matt!