Towards Optimal Multi-Level Checkpointing

We provide a framework to analyze multi-level checkpointing protocols, by formally defining a
$k$
-level checkpointing pattern. We provide a first-order approximation to the optimal checkpointing period, and show that the corresponding overhead is in the order of
$\sum _{\ell =1}^{k}\sqrt{2\lambda _\ell C_\ell}$
, where
$\lambda _\ell$
is the error rate at level 
$\ell$
, and
$C_\ell$
the checkpointing cost at level 
$\ell$
. This nicely extends the classical Young/Daly formula on single-level checkpointing. Furthermore, we are able to fully characterize the shape of the optimal pattern (number and positions of checkpoints), and we provide a dynamic programming algorithm to determine the optimal subset of levels to be used. Finally, we perform simulations to check the accuracy of the theoretical study and to confirm the optimality of the subset of levels returned by the dynamic programming algorithm. The results nicely corroborate the theoretical study, and demonstrate the usefulness of multi-level checkpointing with the optimal subset of levels.