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Wednesday, August 25, 2004
A Very Brief History of Internal IIS Compression
By Brett Hill (brett) @ 6:42 PM :: IISFAQ Front Page :: 7 Comments :: 14115 Views

A Very Brief History of Internal IIS Compression

There are both server-side and client-side bugs that have plagued internal compression for IIS 5 (and IIS 4).

The server-side bugs that make internal IIS compression unusable in most real world environments include: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q313712
(It's misleading because it categorizes it as a browser problem, when in fact it can be corrected on the server, as compression filters do.)

There are also numerous client-side bugs that make internal IIS compression, as it is, practically unusable in most environments. Andy King outlines the nature of these bugs in his short article on HTTP compression:

The root of all of these browser bugs is that they sometimes lie; They claim to handle gzip decompression in all cases (in their accept-encoding header) when in practice they will choke in limited cases. For example, they will break when trying to decompress a specific file type or--even more weird--they might confuse a specific cached compressed file for a decompressed file and try to render the compressed content. Netscape is not the only browser that sometimes lies. In addition to the longstanding, well-known lying browser bugs, new ones continue to creep up, although they are becoming more and more obscure.

The server side bugs were fixed in IIS 6. Lying browsers however are still widespread, so the key is getting a product that includes the browser sensing feature.

In practice, the ability to configure at multiple levels becomes crucial. With web applications of any complexity, being able to easily include/exclude specific files, directories and sites makes the difference between using/not using compression. The built in GUI for IIS compression has historically made this so difficult--actually impossible--that the user's only choice was an all or nothing one. Users would often encounter one of the many bugs and would shut it off and write off compression altogether, forfeiting the many benefits that it offers. In short, the combination of server-side bugs, client-side bugs and an inadequate GUI have sabotaged many efforts to implement internal IIS compression.

My best advice: Before you start looking into compression filters, arm yourself with a good http header sniffer tool (httpWatch is the best, but is a bit pricey) and familiarize yourself with the http layer. Since compression should be totally transparent, it will make evaluation and troubleshooting much easier.

Tad
Port80 Software

Comments
By Wayne 'waynebe' Berry @ 8/31/2004 12:21 PM
If you don't want to "arm yourself with a good http header sniffer tool and familiarize yourself with the http layer." you can just purchase an ISAPI Compression filter that works out of the box. XCompress for IIS http://www.xcache.com uses Smart Compression Technology that advoids browser and server side bug -- making compression truely transparent.

Just a note, XCompress for IIS costs about the same as a support call to Microsoft Product support -- which you will probably have to make if you try to use their compression.

Kind Regards,
Wayne Berry
XCache Tech (makers of XCompress for IIS)




By Chris 'Port80Guy' Neppes @ 9/1/2004 7:49 PM
Chris here from Port80 Software.

It is true that there were issues with IIS 5 native compression on Windows 2000 (and no alternative on IIS 4/NT). This is why a third party market emerged for compression on this platform with tools like Port80's httpZip and Wayne’s offering.

Port80 and XCompress differ fundamentally on our approach to IIS 6.0 compression on Windows Server 2003. Our position is that, as a result of the major changes in IIS 6, compression now works "out of the box" in the majority of cases. IIS 6 compression is also more performant than any ISAPI-based solution because compression is executed in the core Web server code itself.

There was room for improvement. IIS 6 compression needed a richer GUI interface, a wizard and important features like browser compatibility checking (a must for compression) and CPU roll-off (for those who like safety valves). By selectively adding value to IIS 6 native compression, rather than replacing it entirely, Port80 is able to offer a compression solution that costs considerably less than that support call to Microsoft (a call you are unlikely to have to make with IIS 6).

If you are interested in IIS compression and want to save money while using the best-in-class solution, try Port80's ZipEnable and IIS 6 native compression:

http://www.microsoft.com/iis/compression
http://www.zipenable.com

Best,
Chris Neppes
Port80 Software

Enhancing Microsoft IIS Web servers.
security. performance. user experience.

By Josh 'josh2000' T @ 12/17/2004 11:35 AM
Xcache is unable to handle average traffic and randomly sends back unprocessable information to the most standard browsers that result as blank pages. We tested it in two development environments for several weeks. Also there was a bug uninstalling it from one server which messed up the system. IIS6 compression made it from development servers to live now and is perfectly handling a large loads totally uncompareable to the development environment's load which Xcache could not handle.

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