I am planning to start working on adding load management enhancements to distcc for use at our company, but wanted to make sure that no one was almost done fixing the problem and also make sure that I didn't spend a bunch of time making my changes and have them rejected.
I'm about to work on something similar but simpler.
A brief summary of my proposal:
1) have distccd listen on a UDP port for "status requests"
a) when distccd gets a request on this port, send back status info to the requester
1) number of active compilation requests
2) "server weight"
3) maximum connections
4) other status information TBD
b) forking client
1) just look at dcc_nkids variable
c) preforking client
1) have each child lock/unlock a file when it starts/finishes compilation
2) distccd tries to lock each file; number of locked files = number of active connections
3) on startup, distcc determines appropriate server to send request to
a) poll all servers in host list - wait until all respond or 0.1 seconds, whichever comes first
b) multiply connection count by weight, take minimum result, send request to that server
"least connection" loadbalancing actually does a very good job of spreading the load around - faster machines process connections faster and so end up getting more of the work. Weighting is more or less optional, but can be used if you want some machines in the cluster to be dedicated compilation boxes and others are also used for other things.
For starters, I was simply going to have distccd drop incoming connections if the load average was over a threshold. That would achieve my limited goal of avoiding killing workstations that were busy doing other things (as the client would blacklist the busy workstation for a minute). I think I also need to have the client randomize the host list on startup.
I have more ambitious plans, involving a local proxy server, but I'm less likely to do those soon.
I don't think blasting all N servers with a UDP packet on
each distcc run is a good idea. And all my servers are
identical speed, and probably all running just one job,
so they're all either busy or not; no connection counts or
weights to care about.
- Dan
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