September 2007
Intermediate to advanced
170 pages
4h 24m
English
Content preview from High Performance Web SitesBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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The Problem with ETags
The problem with ETags is that they are typically constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later makes a conditional GET request that goes to a different server—a situation that is all too common on web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Inodes are used by
filesystems to store information such as file type, owner, group, and
access mode. Although a given file may reside in the same directory
across multiple servers and have the same file size, permissions,
timestamp, etc., its inode is different from one server to the
next.
IIS 5.0 and 6.0 have a similar issue with ETags. The format for
ETags on IIS is Filetimestamp:ChangeNumber. ChangeNumber is a counter used to track
configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS
servers behind a web site.
The end result is that ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.