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From Igor Galić <i.ga...@brainsware.org>
Subject Re: Caching - Generating E-Tags
Date Sun, 09 Oct 2011 22:10:45 GMT


----- Original Message -----
> 
> Am 06.10.2011 19:03, schrieb Amila Liyanaarachchi:
> > Hi Dev,
> > 
> > I'm working on a caching protocol similar to HTTP on a different
> > research. I have the following question regarding
> > the e-tags.
> > When does exactly apache computes the e-tag for a certain resource?
> > Does it compute that when there is a request for that particular
> > resource or is it computed by the server whenever
> > a resource get modified in the server?
> 
> request time because it normally contains the inode

Which makes it quite useless in a farm with multiple servers
as the same files will have different inodes.

My recomendation is to use size and mtime:

http://httpd.apache.org/docs/current/mod/core.html#fileetag

ETag is then an MD5 sum of a combination of all values considered.

Be wary that the calculation of the ETag can sometimes take more
effort than just delivering the ETag.

See Theo Schlossnagle's performance talks for reference:
http://omniti.com/seeds/yslow-to-yfast-in-45-minutes
http://lethargy.org/~jesus/writes/web-performance-boot-camp


i

-- 
Igor Galić

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Mail: i.galic@brainsware.org
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