The OBIEE 11g UI is performance is slow in IE 8 and faster in Firefox.  For VPN or WAN users, it takes long time to display links on Dashboards via IE 8. Cause is IE 8 generates many HTTP 304 return calls and this caused the 11g UI slower when compared to the Mozilla FireFox browser.

To resolve this issue, you can implement HTTP compression and caching. This is a best practice.

Why use Web Server Compression / Caching for OBIEE?

• Bandwidth Savings: Enabling HTTP compression can have a dramatic improvement on the latency of responses. By compressing static files and dynamic application responses, it will significantly reduce the remote (high latency) user response time.

• Improves request/response latency: Caching makes it possible to suppress the payload of the HTTP reply using the 304 status code.  Minimizing round trips over the Web to re-validate cached items can make a huge difference in browser page load times.

This screen shot depicts the flow and where the compression and decompression occurs:

Solution:

a. How to Enable HTTP Caching / Compression in Oracle HTTP Server (OHS) 11.1.1.x

1. To implement HTTP compression / caching, install and configure Oracle HTTP Server (OHS) 11.1.1.x for the bi_serverN Managed Servers (refer to "OBIEE Enterprise Deployment Guide for Oracle Business Intelligence" document for details).

2. On the OHS machine, open the file HTTP Server configuration file (httpd.conf) for editing. This file is located in the OHS installation directory.
For example: ORACLE_HOME/Oracle_WT1/instances/instance1/config/OHS/ohs1

3. In httpd.conf file, verify that the following directives are included and not commented out:

4. Add the following lines in httpd.conf file below the directive LoadModule section and restart the OHS:

Note: For the Windows platform, you will need to enclose any paths in double quotes ("), for example:
Alias "/analytics ORACLE_HOME/bifoundation/web/app"
<Directory "ORACLE_HOME/bifoundation/web/app">

Alias /analytics ORACLE_HOME/bifoundation/web/app
#Pls replace the ORACLE_HOME with your actual BI ORACLE_HOME path
<Directory ORACLE_HOME/bifoundation/web/app>
#We don't generate proper cross server ETags so disable them
FileETag none
SetOutputFilter DEFLATE
# Don't compress images
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary
<FilesMatch "\.(gif|jpeg|png|js|x-javascript|javascript|css)$">
#Enable future expiry of static files
ExpiresActive on
ExpiresDefault "access plus 1 week"     
#1 week, this will stops the HTTP304 calls i.e. generated by IE 8
Header set Cache-Control "max-age=604800"
</FilesMatch>
DirectoryIndex default.jsp
</Directory>

#Restrict access to WEB-INF
<Location /analytics/WEB-INF>
Order Allow,Deny
Deny from all
</Location>

Note: Make sure you replace above placeholder "ORACLE_HOME" to your correct path for BI ORACLE_HOME.
For example: my BI Oracle Home path is /Oracle/BIEE11g/Oracle_BI1/bifoundation/web/app

Important Notes:

• Above caching rules restricted to static files found inside the /analytics directory(/web/app).
• This approach is safer instead of setting static file caching globally.
• In some customer environments you may not get 100% performance gains in IE 8.0 browser. So in that case you need to extend caching rules to other directories with static files content.
• If OHS is installed on separate dedicated machine, make sure static files in your BI ORACLE_HOME (../Oracle_BI1/bifoundation/web/app) is accessible to the OHS instance.

The following screen shot summarizes the before and after results and improvements after enabling compression and caching: