Xiao Liu PhD Thesis.pdf - Faculty of Information and Communication ...

Chapter 4 and Chapter 5 respectively.
The second component is temporal consistency monitoring which deals with
monitoring of temporal consistency state against temporal violations. Based on a
temporal consistency model, the temporal consistency states of scientific cloud
workflows should be under constant monitoring in order to detect potential temporal
violations in a timely fashion. However, as mentioned before, the cost of temporal
verification can be very huge due to the complexity and uncertainty in cloud
workflow system environments. Therefore, cost-effective strategies need to be
designed to detect potential temporal violations in an efficient fashion.
In our framework, the function of temporal consistency state monitoring is
realised through a two-step process. The first step is temporal checkpoint selection.
Given the probability based temporal consistency model, our minimum probability
time redundancy based checkpoint selection strategy can choose the minimal set of
activity points (i.e. necessary and sufficient checkpoints) for temporal verification.
The second process is temporal verification which checks the current temporal
consistency states at the selected checkpoints with our probability based temporal
consistency model. In our temporal framework, instead of conventional four types of
checkpoint and temporal consistency states, only one type of checkpoint and
temporal consistency state (i.e. recoverable state) needs to be verified, and thus
reduce the cost of checkpoint selection and temporal verification. The detailed
process will be introduced in Section 3.3 and the algorithms will be further
presented in Chapter 6.
The third component is temporal violation handling which deals with recovery of
temporal violations. Based on the results of the previous component for monitoring
temporal consistency, a necessary and sufficient checkpoint is selected where a
potential temporal violation is detected. Conventional temporal verification work
believes in the philosophy that temporal violation handling should be executed at all
necessary and sufficient checkpoints. However, given the probability of selfrecovery
(i.e. the time deficit can be automatically compensated by the saved
execution time of the subsequent workflow activities), we have identified that such a
philosophy is not necessarily ideal. Therefore, a temporal violation handling point
selection process should be designed to further determine whether temporal
violation handling is necessary at each checkpoint. Here, necessity for temporal
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