[Swift-devel] Re: replication vs site score

[Mihael Hategan]

On Mon, 2009-04-06 at 14:39 +0000, Ben Clifford wrote:
> even more rambling... in the context of a scheduler that is doing things 
> like prioritising jobs based on more than the order that Swift happened to 
> submit them (hopefully I will have a student for this in the summer), I 
> think a replicant job should be pushed toward later execution rather than 
> earlier execution to reduce the number of replicant jobs in the system at 
> any one time.

You have two extremes:
1. Send each job to all sites instantly.
2. Replicate after +inf time (see _too_much_ below)

You're suggesting moving from somewhere in the middle, to somewhere in
the middle, but a little to the right.

> 
> This is because I suspect (though I have gathered no numerical evidence) 
> that given the choice between submitting a fresh job and a replicant job 
> (making up terminology here too... mmm), it is almost always better to 
> submit the fresh job. Either we end up submitting the replicant job 
> eventually (in which case we are no worse off than if we submitted the 
> replicant first and then a fresh job); or by delaying the replicant job we 
> give that replicant's original a chance to start running and thus do not 
> discard our precious time-and-load-dollars that we have already spent on 
> queueing that replicant's original.

You are saying this with the awareness of the fact that replicas are
only sent after the prototype job sat in the queue (and didn't start
running) for what is deemed _too_much_?