Etag/Last Modified - the numpty question I've always wanted to know.

[pmeenan]

It's actually a little more fringe than that. You need to be running a site that has multiple servers serving the same files and those servers would have to be using an Apache config with the default etag behavior (that includes machine-specific information in the hash or at least used to).

In this worst-case scenario, it's possible that when the conditional e-tag check is made, instead of a "not modified", the server will send the full file.

It's such a fringe condition that it's not really worth investing any time into and I'll be removing it from the checks to eliminate confusion (or premature optimization).

Thanks,

-Pat