Xiao Liu PhD Thesis.pdf - Faculty of Information and Communication ...
Xiao Liu PhD Thesis.pdf - Faculty of Information and Communication ...
Xiao Liu PhD Thesis.pdf - Faculty of Information and Communication ...
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PTDA+ACOWR as an example to introduce the temporal violation h<strong>and</strong>ling process.<br />
The details about these strategies will be presented in Chapter 8.<br />
For PTDA+ACOWR, Step 2.1 is to allocate probability time deficit. Based on<br />
PTDA, the occurred time deficit is allocated proportionally to the workflow<br />
activities <strong>of</strong> the subsequent local workflow segment. The purpose <strong>of</strong> time deficit<br />
allocation is to ensure the balance among the subsequent workflow activities to<br />
share the time deficit. Unlike the conventional strategy which assigns the time<br />
deficit to all the workflow activities remained in the workflow instance [17], our<br />
strategy only considers the subsequent local workflow segment after the selected<br />
h<strong>and</strong>ling point. Therefore, the number <strong>of</strong> workflow activities involved in the<br />
workflow rescheduling process is significantly reduced <strong>and</strong> thus can save the<br />
temporal violation h<strong>and</strong>ling cost.<br />
Step 2.2 is to generate an integrated Task-VM list. The integrated Task-VM list<br />
represents the current scheduling plan for the activities in the local workflow<br />
segment <strong>and</strong> their co-allocated tasks. Since the rescheduling <strong>of</strong> workflow activities<br />
in the local workflow segment will not only change the task assignment <strong>of</strong> their own<br />
but also inevitably change the task assignment <strong>of</strong> other co-allocated tasks. Therefore,<br />
if we do not consider the other co-allocated tasks, their execution time will probably<br />
be delayed <strong>and</strong> may even violate their own temporal constraints, if any. The purpose<br />
for the integrated Task-VM list is to consider all the tasks <strong>and</strong> virtual machines that<br />
will be affected in the rescheduling process. In such a case, a balance between the<br />
time compensation <strong>of</strong> violated workflow instance <strong>and</strong> the overall efficiency <strong>of</strong> the<br />
cloud workflow system could be achieved. Details about the integrated Task-VM list<br />
will also be presented in Section 8.3.1.<br />
Step 2.3 is to optimise the workflow local scheduling plan. The target <strong>of</strong> the<br />
optimisation process is to reduce the execution time <strong>of</strong> the activities in the local<br />
workflow segment so that the occurred time deficit can be compensated. In our twostage<br />
workflow local rescheduling strategy, there are two searching processes. The<br />
first searching process is a metaheuristics based searching process where the overall<br />
makespan <strong>and</strong> cost for the integrated Task-VM list are being optimised. Here, two<br />
representative metaheuristics including GA <strong>and</strong> ACO are investigated. As for the<br />
second searching process, selected valid c<strong>and</strong>idates (scheduling plans) are compared<br />
in order to find the best solution where the execution time <strong>of</strong> the local workflow<br />
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