I've been reading this book (highly recommended):
And I have a particular question about the ETag chapter. The author says that ETags might harm performance and that you must tune them finely or disable them completely.
I understand the risks, but is it that hard to get ETags right?
I've just made an application that sends an ETag whose value is the MD5 hash of the response body. This is a simple solution, easy to achieve in many languages.
My question is: Is this wrong? if so, why? and why the author (who obviously outsmarts me by many orders of magnitude) does not propose such a simple solution?
Thanks
EDIT Please Read!
People are misunderstanding the question. I already know what ETags are, I'm just asking if a MD5 hash of the response body is fine enough, and if so why is not encouraged on the book? This last question is hard to answer unless you are the author :) so I'm trying to find the weak points of using a MD5 hash as an ETag.