WebPagetest Forums
Etags vs. Last Modified Header - Printable Version

+- WebPagetest Forums (https://www.webpagetest.org/forums)
+-- Forum: Web Performance (/forumdisplay.php?fid=3)
+--- Forum: Optimization Discussions (/forumdisplay.php?fid=5)
+--- Thread: Etags vs. Last Modified Header (/showthread.php?tid=11608)

Etags vs. Last Modified Header - trx - 08-30-2012 09:32 AM

Hello ,
After reading online sources (Yahoo, Google etc.) about Etags, I'm still NOT sure I really understand about why Etags were created and what websites can gain from it. It would seem that the "Last-Modified" header should do the trick to determine when a static resource needs to be downloaded back to the client machine and cached again or NOT; so in what case does that method fails and Etags need/can to be used? Maybe there's a scenario that I am missing that would be good to use Etags!???!

Thanks advance.


RE: Etags vs. Last Modified Header - pmeenan - 08-30-2012 09:40 AM

The main place they are helpful is if you have more dynamic or generated data rather than your typical static assets. You can hash or otherwise tag the result and if the hashes match you don't need to transfer all of the data. It is a pretty specific case though so in "general" you shouldn't use them or see them unless you know why you are using it.

RE: Etags vs. Last Modified Header - trx - 08-30-2012 09:47 AM

Thanks make sense. I'm just not sure why Yahoo isn't too clear about what you just stated.