bhat.log() > web

Enabling compression in Web Servers

On a site serving static content or content that are read only, generally does
not generate large data to be consumed by the client. Even in case of large
documents/articles/content most of the sites split the content across multiple
pages to ease the amount of data to be downloaded. In case of applications with
web interfaces this can be different. Generally the users of the system have
been used to a client-server based applications with UI interface with many
smart tricks on the client side. A typical user expects the same behaviour on
the web solution. A clever UI designer can design an interface which works well
even in the web based mode.

But there are many cases where a small thin interface is difficult to design.
Standard examples are dashboard, reporting page or cases where filters are
removed, etc …

For these cases it is a good idea to enable stream compression at the web server
level. This can drastically reduce the bandwidth requirement and hence download
speeds for a site.

Few gotchas:

• Enabling compression will increase the server CPU load. But in a cluster
  enviroment, I definetly recommend this. As a general thumb rule if the server
  machine is running at the max load of 80% enable the compression, otherwise add
  another machine to your cluster environment before enabling them.

• There are browser quirks where these can create problem. Most notable Netscape
  4.xx (these can be safely ignored) or IE 5.5 (yikes, baad browser. If your
  users have this browser, recommend IE 5.5 SP2) or IE 6.0 Japanese version (similar to IE
  5.5 in bugs!)

• Compressing streams smaller then 1K will create unnecessary load on the server.
  If possible disable compression for streams smaller then ~500-1000 bytes.

There is a decent article covering the same here. I will not cover the same points already discussed out there, but these are my take:

• Set compression for both static and dynamic files.

• Disable compression for those aspx or server script files where we serve
  already compressed files. e.g. jpeg, mpeg, dwf, jpg, jpe, gif, zip, cab, mpg,
  mpe, mp3, png, amp, ptp, dwp, pnp, and zgl.

• Understand the following variables of IIS:
  HcDoDynamicCompression,
  HcNoCompressionForRange, In fact readup on
  IIsCompressionSchemes.

• To disable compression for certain files or nodes, set the DoDynamicCompression
  to false.

e.g. scripts:
[code]
C:/Inetpub/AdminScripts/adsutil.vbs set w3svc/{siteID}/root/DoStaticCompression True

cscript C:/Inetpub/AdminScripts/adsutil.vbs set w3svc/{siteID}/root/DoDynamicCompression True

cscript C:/Inetpub/AdminScripts/adsutil.vbs set
W3SVC/{siteID}/root/{subfolder}/{page.aspx}/DoDynamicCompression False
[/code]

Otherwise you can use the Metabase Explorer to do this.

Apache web server

There are two modules available, namely “deflate” and “gzip”.

As the following thread explains if you have Apache 2, use mod_deflate otherwise depending upon your configuration requirements go for either.

The apache site contains information for deflate (http://httpd.apache.org/docs-2.0/mod/mod_deflate.html)
and mod_gzip is explained at http://www.schroepl.net/projekte/mod_gzip/config.htm

A sample configuration
[code]
mod_gzip_on Yes

mod_gzip_on Yes
#mod_gzip_send_vary Yes
mod_gzip_add_header_count Yes
mod_gzip_dechunk Yes

mod_gzip_can_negotiate Yes
mod_gzip_update_static No
mod_gzip_static_suffix .gz

mod_gzip_minimum_file_size 300
mod_gzip_maximum_inmem_size 60000
mod_gzip_maximum_file_size 2000000
mod_gzip_temp_dir /tmp
mod_gzip_keep_workfiles No

## minimal included set of items to compress to avoid sending Vary * header
## This is very conservative and cooperates superbly with mod_expires
## caching headers. (Netscape 4.0[678] will still have problems, but it
## only affects a fraction of a percent of hits (about 0.00015 == 0.015%)
## on our site with the settings below)
mod_gzip_item_include uri .s?html?$
mod_gzip_item_include mime ^text/
mod_gzip_item_include file .php$
mod_gzip_item_include file .js$
mod_gzip_item_include file .css$

mod_gzip_item_exclude mime ^image/

[/code]