Patent Application: US-51470606-A

Abstract:
in the context of problems associated with self - healing in autonomic computer systems , and particularly , the problem of fast and efficient real - time diagnosis in large - scale distributed systems , a “ divide - and - conquer ” approach to diagnostic tasks is disclosed . preferably , parallel and distributed architectures are used , whereby the diagnostic task is preferably divided into subtasks and distributed to multiple diagnostic engines that collaborate with each other in order to reach a final diagnosis . each diagnostic engine is preferably responsible for some subset of system components and performs the diagnosis using all available observation about these components . when the regions do not intersect , the diagnostic task is trivially parallelized .

Description:
although a general approach is broadly contemplated herein , which can be applied to a very wide variety of prospective environments , the disclosure now turns to a specific example of example of a “ probing ” approach to problem diagnosis [ 2 , 3 ]. a “ probe ”, as may be broadly understood for the discussion herein , is an end - to - end transaction ( e . g ., ping , webpage access , database query , an e - commerce transaction , etc .) sent through the system for the purposes of monitoring and testing . usually , probes are sent from one or more probing stations ( designated machines ), and ‘ go through ’ multiple system components , including both hardware ( e . g . routers and servers ) and software components ( e . g . databases and various applications ). formally , one may consider a set x ={ x 1 , . . . , x n } of system components , a set t ={ t 1 , . . . , t m } of tests ( probes ), and an m n × dependency matrix [ d ij ] where the columns correspond to the components , the rows correspond to the probes , and d ij = 1 if executing probe i involves component j , and 0 otherwise . for example , fig1 shows a simple network with 2 probe stations at nodes 1 and 6 , and a dependency matrix including 3 probes . in the presence of noise , different prior fault probabilities , and multiple failures , one may preferably apply a probabilistic approach to diagnosis that can use a convenient framework of bayesian networks . the dependency matrix can be mapped to a two - layer bayesian network [ 4 ] where the states of components x i correspond to upper - level variables and the probes t i correspond to the lower - layer variables , whose parents are the components influencing the probe &# 39 ; s outcome and specified by 1 in corresponding row of the dependency matrix . for example , fig1 shows such a bayesian network corresponding to the dependency matrix above . in this example , it is assumed that components x i are marginally independent , and each probe outcome depends only on the components tested by this probe . these assumptions yield a joint distribution p ( x , t )= π i = 1 n p ( x 1 ) π j = 1 m p ( t j | pa ( t j )) where p ( x i ) is a prior distribution of x i . given the probe outcomes , diagnosis consists in finding most - likely combination of faults that “ explain ” the observed probe outcomes . unfortunately , solving this problem exactly can be computationally expensive or even impossible as the exact inference is known to be an np - hard problem . thus , in accordance with at least one presently preferred embodiment of the present invention , a “ belief propagation ” algorithm is preferably employed as a tool of approximation . preferably , this tool is can also easily be parallelized and thus be implemented in distributed fashion ( especially desirable if one prefers to off - load a central management server ). belief propagation ( bp ), in essence , may be thought of as a simple linear - time message - passing algorithm that is provably correct on polytrees ( i . e ., bayesian networks with no undirected cycles ) and that can be used as an approximation on general networks . preferably , belief propagation passes probabilistic messages between the nodes and can be iterated until convergence ( guaranteed only for polytrees ); otherwise , it can be stopped at a given number of iterations . the algorithm computes approximate beliefs p ( x i | t ) for each node . by way of a simple ( and non - restrictive ) example , one may consider a network where several nodes are designated diagnostic nodes ( called rail — real - time active inference and learning engine nodes ), with associated epp ( end - to - end probing software ); this is schematically illustrated in fig2 . in this example there are three rail nodes each with associated epp , in addition to six “ standard ” nodes x 1 . . . x 6 . in turn , the problem illustrated in fig2 can be represented a bayesian network as shown in fig3 . preferably , iterative belief propagation works by sending messages between nodes and updating probabilities ( also called beliefs ) at every node , as shown in fig4 . assuming that there are several diagnostic engines ( e . g ., multiple rail systems ) controlling different subsets of components then , desirably , the subsets will be made independent so that the inference problem would trivially decompose . however , in practice , this may not always be possible . for example , in considering the probing approach , let it be assumed that each diagnostic engine is making inferences based on its own subset of probes , as shown in fig5 . here rail 1 receives probes t 1 and t 2 and therefore diagnoses nodes { x 1 , x 2 , x 3 , x 5 , x 6 }, while rail 2 received probe t 3 and diagnoses nodes { x 2 , x 3 , x 4 }. thus , the subsets of nodes intersect due to probe intersection ( which is quite common , especially when a probe set needs to be optimized so that a minimal number of probes covers the system ) and therefore beliefs obtained by different diagnostic engines about these nodes must be combined . such combination can be brought about naturally by applying belief propagation in a distributed way , so that each rail will be responsible for keeping and updating messages related to its nodes . clearly all factor nodes in the corresponding factor graph that involve a rail &# 39 ; s nodes will belong to that rail as well . preferably , a system architecture ( generally , a hierarchical one ) will be employed that is a publish - subscribe architecture for message exchange between different diagnostic / monitoring nodes ( peers , also called rails above ) through higher - level “ councilors ”, using “ message patterns ” that describe which messages and where should be sent by each rail , and which messages it expects to receive from its peers . preferably , the system topology ( as shown in fig6 ) includes three tiers of nodes wherein : the bottom tier contains the peer nodes which are actually diagnosis engines and iteratively calculate and update the beliefs of system states for covered components ; the middle tier contains the super - peer nodes , also called councilors , which are centralized servers to their subsets of peers and hold a publication / subscription ( abbreviated as pub / sub ) pool ( one per councilor ) for the purpose of sharing information among local peers ; and the top tier contains a metaserver node playing the role of bootstrapping node , providing monitor services , keeping an index directory for all councilors and a pub / sub pool for sharing information globally . in a real system , a node can be both councilor and peer or both councilor and metaserver depending on the size of network . preferably , dynamic message patterns are also supported in order to handle changes in the system , such as leaving and joining nodes both in the system under control and in our diagnostic infrastructure ( e . g ., addition of new rail engines , or unexpected failure of such an engine ). it is to be understood that the present invention , in accordance with at least one presently preferred embodiment , includes elements that may be implemented on at least one general - purpose computer running suitable software programs . these may also be implemented on at least one integrated circuit or part of at least one integrated circuit . thus , it is to be understood that the invention may be implemented in hardware , software , or a combination of both . if not otherwise stated herein , it is to be assumed that all patents , patent applications , patent publications and other publications ( including web - based publications ) mentioned and cited herein are hereby fully incorporated by reference herein as if set forth in their entirety herein . although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings , it is to be understood that the invention is not limited to those precise embodiments , and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention . s . kliger , s . yemini , y . yemini , d . ohsie , and s . stolfo . a coding approach to event correlation . in intelligent network management ( im ), 1997 . i . rish , m . brodie , n . odintsova , s . ma , g . grabarnik , real - time problem determination in distributed systems using active probing , in proceedings of noms - 2004 , seoul , korea , april 2004 . a . frenkiel and h . lee . epp : a framework for measuring the end - to - end performance of distributed applications . in proc . performance engineering best practices conference , ibm academy of technology , 1999 . j . s . yedidia , w . t . freeman , and y . weiss , constructing free energy approximations and generalized belief propagation algorithms , technical report tr - 2004 - 040 , merl , may 2004 . m . welsh , d . culler , and e . brewer , seda : an architecture for well - conditioned scalable internet service , in proceedings of the 18th acm symposium on operating systems principles , october 2001 . i . clarke , o . sandberg , b . wiley , and t . w . hong . freenet : a distributed anonymous information storage and retrieval system . in designing privacy enhancing technologies : international workshop on design issues in anonymity and unobservability . springer , new york , 2001 b . yang , h . garcia - molina , designing a super - peer network , proceedings of icde , 2003 . i . stoica , r . morris , d . karger , f . kaashoek , and h . balakrishnan , chord : a scalable peer - to - peer lookup service for internet applications , proceedings of acm sigcomm &# 39 ; 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