Monday, May 25, 2009
On Parallel processing and Event Processing - Take I
My travels in the universe have taken me to Brussels (somehow, I have never been in Belgium), for meetings regarding an EU project we intend to propose for the next call, I'll Blog about this proposal when it will be more mature. As we are working for a while on parallel processing related to event processing, I am looking at some of the related work. I came across an interesting article in Gregor Hohpe's Blog, stating some of the assumptions behind the parallel programming model of cloud computing. Gregor defines these assumptions as the "new ACID", relating to the old ACID properties of transaction correctness (Atomicity, Consistency, Isolation, Durability). Gregor provides four new ACID properties for the cloud computing: Associative, Commutative, Idempotent, Distributed. Gregor explains the notions:
While the original ACID properties are all about correctness and precision, the new ones are about flexibility and robustness. Being associative means that a chain of operations can be performed in any order, the classical example being (A + B) + C = A + (B + C) for the associative operator ‘+’. Likewise, we remember commutative from junior high math as A + B = B + A, meaning an operator can be applied to a pair of operands in either direction. Finally, a function is idempotent if its repeated application does not change the result, i.e. f(x) = f(f(x)).Having these properties enable paralleling the operations and collecting the results, the principle behind Google's MapReduce. In order to take advantage of this way of parallelism for event processing functions (or agents), we need to check whether these properties are satisfied. In event processing -- the temporal dimension and the fact that some of the patterns are not associative, some are not commutative, and some are not idempotent, may issue a challenge. This does not say that the parallelism idea is not valid for event processing applications, it is just saying that the parallelism is influenced from the semantics of the event processing network. I'll drill down into this issue in future postings.