It's not the etag calc it's actually the round tripping to the server
that is the main over head - better to get the client to cache content...
Apache will still have to touch the file system to see if the content
has changed (however it is done) and on some filesystems just
locating the file and making sure the user can read it is slower than
serving it (especially high availability and virtual file systems)...
James
On 09/06/2015 14:51, Frederik Nosi wrote:
Hi Rainer,
On 06/09/2015 02:53 PM, Rainer Canavan wrote:
Remove etags (Header unset Etag/FileETag None)
Won't this disable conditional requests, ex. If-None-Match and
friends? Is
your recomendation because of the header overhead or am I missing
something?
Just if-None-Match. If-Modified-Since would still work. I believe
people recommend disabling ETags because they may cause problems with
clusters (i.e. different inode numbers or modification times for
otherwise identical files), or gzip content encoding
(https://bz.apache.org/bugzilla/show_bug.cgi?id=45023).
Well, if it's a static file i think the etag calculation should be
quite fast, after all in the default apache setting it's computed
using thre values:
FileETag INode MTime Size
which at least on linux should be cached in the dentry / filesystem
cache.
So intuitively should be less work then reading this values, the file
content and sending it.
It's not that i've done measurements on this though, just speculation.
As for the cluster case (and for security reasons), i've been using:
FileETag MTime Size
Out of curiosity, does somebody have real misurements?
rainer
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