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From Darryl Miles <>
Subject Re: mod_proxy_balancer/mod_proxy_ajp TODO
Date Thu, 22 Jun 2006 12:55:07 GMT
Henri Gomez wrote:

> Well you we always indicate some sort of CPU power for a remote (a sort 
> of bogomips) and use this in computation.

Why should the CPU power matter, what if the high power CPU is getting 
all the complex requests and the lower power CPU is ending up with 
simple request (static content).

You are better implementing it in control packets over AJP that can 
advertise that hosts current willingness to take on new requests on a 
32/64bit scale.  Call this a "flow control back pressure packet", a 
stateless beacon of information which may or may not be used by the 
client AJP.

Then have a pluggable implementation at the server end of calculating 
that value and frequency for advertising it.  All the apache LB has to 
do is work from that load calculation.  All existing AJPs have to do is 
just ignore the packet.

In the case of different horse power CPUs that factor is better fed into 
the server AJP algorithm by biasing the advertised willingness to take 
on new requests after a certain low level is reached.  Only the server 
end of the AJP know the true request rate and how near that system is to 
breaking point.

This scheme also works where apache may not see all the work the backend 
is doing, like if you have a different apache front end clusters linked 
to the same single backend cluster.


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