If the cache for a given channel needs to get regenerated in /var/cache/rhn every client request for that new metadata kicks of a process to regenerate the files.

This can cause extreme load on the Satellite server and each thread is essentially doing the same thing.

In order to reproduce this issue I wrote a simple multi-threaded python utility to spawn multiple yum requests to a RHN Satellite server.  This client spins up 10 threads each doing:

yum clean all && yum search zsh

with separate --installroot parameters to allow simultaneous execution.

After setting up 2 RHEL5 clients each with my load simulator I was 
quickly able to get my Satellite to reach a load of *40-80* with it 
eventually ceasing to be accessible.

** Steps to reproduce the yum 'metadata storm' on a 5.2 Satellite:

1) Register at least 2 RHEL5 clients to your Satellite

2) Make sure your RHEL5 channel is populated and synced

3) Check out: 
http://svn.rhndev.redhat.com/viewcvs/trunk/eng/scripts/load-testing/yum-load-test.py

4) On each RHEL5 client as root execute: 'python yum-load-test.py'

5) On your RHN Satellite server run: 'rm -rf /var/cache/rhn/'

6) wait .. This will cause each client request to start re-generation of 
the metadata for the rhel5 channel.  As these requests pile up the 
server is quickly brought to its knees.

The more clients you have the quicker it will die.