We propose two extensions for a state-of-the-art method of rollback-recovery in distributed CEP (complex event processing). In CEP, an operator network is used to search for patterns in events streams. Sometimes these operators fail and lose their state. Rollback-recovery is a method for dealing with such state losses. The type of rollback-recovery we consider is upstream backup, where the state of a failed operator is recovered by replaying to it the input events that led it to that state. These events are kept in upstream operators' memory buffers, which are trimmed continuously as the downstream operator progresses. The first extension we propose saves memory and speeds up recovery by avoiding to store and retransmit unnecessary events. The second extension makes the base method of upstream backup compatible with dataparallel CEP, allowing that the windows into which operators partition their input be processed in parallel. We evaluated the proposed extensions through experiments that showed a significant reduction in memory usage and recovery time at the expense of a negligible processing overhead during normal operation.

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Almeida,Vitor Pinheiro de; Endler, Markus (Advisor). DSCEP: An Infrastructure for Decentralized Semantic Complex Event Processing.

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In this paper, we investigate the problem of normal forms for links and connectors in NCL 3.0. We identify two such forms, called the First and Second Normal Forms (NF1 and NF2), in which links and connectors appear in simple terms. We also present normalization procedures (proofs), which show that for every NCL 3.0 program, there is an equivalent program in each of the forms. The mere existence of NF1 and NF2 makes the semantic analysis of programs simpler. Moreover, the symmetry exhibited by these forms suggests that the same principle of arbitrarily ordered evaluation underlies both the evaluation of link conditions and the execution of nonsequential compound actions.