[distcc] Suggestion about host selection

Nils Klarlund klarlund at google.com
Thu Jun 19 19:33:42 GMT 2008

> Where is that flag? Randomized selection sounds good. What about
> using an exponential distribution, which prefers slots towards the
> start of the list? Would be easy to implement.

See the disttc(1) of distcc 3.0 or


this is one of the patches we've used at Google for some time.

 The major omission in the current code, in my opinion, is that
> randomization does not take into account the specified host slots.

OK, that would be something to change then.
> It would be fine if one could list a host multiple times (which would
> emulate the behavior I was looking for). This is not possible currently.
> The easiest way for a better selection implementation would be to
> first expand the host/slotcount list to a list of host/slotnumber
> pairs and then select
> a) linearly from the front
> b) with exponential random distribution
> c) with uniform random distribution
> d) ... what ever else may seem appropriate
> I think that simply interpreting the slotnumber as a weight for a uniform
distribution is all what's needed in practice.

To really improve scheduling for smaller installations there's is probably
other more important low-hanging fruit such as the enjoyed-host logic that
disables the selection of a host for a couple of minutes -- whatever the
reason for compilation failure is.

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