"if modified since" and google
I've been practicing a bit of php lately, especially things relating to http headers. While I was at first a bit annoyed that there was no easy way to detect the http headers in php4. there's a get_headers, but apparently this is only implemented in php5.
I did, however, stumble into something else while searching for it. since I was going over and over the headers section in the php manual, I noticed that you can send out the last modified header.
since this could be so easily abused (you'd just have to have it send out the correctly modified current date/time), I assumed there was no way google or other search engines could possibly use this much at all. however, apparently I'm wrong, googleguy endorses its use.
interesting, to say the least. drawbacks of doing a modified since "hack"? more bandwidth (if you want some sort of medium, you could have it be changed on a certain frequency, not all the time). but hey, that's not too much to ask for in exchange for more frequent visits, is it?
1 Comments:
Yeah it's certainly interesting, I've been thinking about the same thing recently.
I'm of the opinion that if the last modified header changes too frequently then Google will more than likely have a filter to identify abuse of this header.
Take a moment to consider that this header is designed to show the last modified date of a FILE not necessarily the content output to the screen.
So even if you ran a PHP forum with constantly updated posts etc your last modified header would not necessarily change daily or hourly.
This is only theoretical, but imagine if you ran a large HTML only content site where you were constantly changing the actual documents themselves then you might see the Googlebot decline in it's visits despite a constantly updated 'modified header'. But again, if it was a large website it's very unlikely that you would be physically able to update all the HTML documents daily. So a filter like this would be quite relevent...
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