To assess the variability of per-node available resources over time, we ask what fraction of nodes that meet a particular resource requirement at time T continue to meet that requirements for all time intervals between T and T+x, for various values of x and all times T in our trace. If the fraction is large, then most slivers initially deployed to nodes meeting the requirement at time T will find themselves continuously executing on nodes that meet the requirement until time T+x. Conversely, if the fraction is small, then most slivers will find the resource requirement violated at some time before T+x, suggesting that they may benefit from migration at a time granularity on the order of x.
Figures 12 and 13 show the fraction of nodes that meet a particular resource requirement at time T that continue to meet the requirement for all time intervals between T and T+x, for various values of x, averaged over all starting times T in our trace. The fraction of nodes that continually meet initial requirements declines rapidly with increasing intervals x, and the rate of decline increases with the stringency of the requirement. Most importantly, we see that the fraction of nodes continually meeting typical resource requirements remains relatively high (80% or greater) up to about 30 minutes post-deployment for load and up to about 60 minutes post-deployment for network traffic. This result suggests that if sliver resource requirements remain relatively constant over time, then it is unnecessary to migrate more often than every 30 to 60 minutes.
Figure 12: Fraction of nodes continuously meeting various load constraints for various durations after initially meeting the constraint. The fraction is 100% at x=0 because we consider only nodes that initially meet the constraint.
Figure 13: Fraction of nodes continuously meeting various constraints on network transmit bandwidth from competing applications for various durations after initially meeting the constraint. The fraction is 100% at x=0 because we consider only nodes that initially meet the constraint. Similar results were found for receive bandwidth.
David Oppenheimer 2006-04-14
