Soft-Checkpointing Based Hybrid Synchronous Checkpointing Protocol for Mobile Distributed Systems

Minimum-process coordinated checkpointing is a suitable approach to introduce fault tolerance in mobile distributed systems transparently. In order to balance the checkpointing overhead and the loss of computation on recovery, the authors propose a hybrid checkpointing algorithm, wherein an all-process coordinated checkpoint is taken after the execution of minimum-process coordinated checkpointing algorithm for a fixed number of times. In coordinated checkpointing, if a single process fails to take its checkpoint; all the checkpointing effort goes waste, because, each process has to abort its tentative checkpoint. In order to take the tentative checkpoint, an MH (Mobile Host) needs to transfer large checkpoint data to its local MSS over wireless channels. In this regard, the authors propose that in the first phase, all concerned MHs will take soft checkpoint only. Soft checkpoint is similar to mutable checkpoint. In this case, if some process fails to take checkpoint in the first phase, then MHs need to abort their soft checkpoints only. The effort of taking a soft checkpoint is negligibly small as compared to the tentative one. In the minimum-process coordinated checkpointing algorithm, an effort has been made to minimize the number of useless checkpoints and blocking of processes using probabilistic approach.