S-CUBE LP: Using Data Properties in Quality Prediction
S-Cube Learning PackageUsing Data Properties in Quality Prediction ´ Universidad Politecnica de Madrid (UPM)
Learning Package Categorization S-Cube WP-JRA-1.3: End-to-End Quality Provision and SLA Conformance Quality Assurance and Quality Prediction Using Data Properties in Quality Prediction
Service Compositions and QoS Service compositions are an essential element of the Service-Oriented-Architecture (SOA): • Putting together several “lower level” (specialized) services • Leveraging low coupling and platform-independence • Achieve a more complex goal, e.g. a business process • Often cross-organizational, i.e. using services from different providers Quality of Service (QoS) for compositions often critically important: • Relates to composition level running time, computational cost, bandwidth, etc. • Depends on QoS of component services + composition internals + environment factors (such as system and network loads/failures) • Can affect business-level KPIs (key performance indicators) • Inﬂuences applicability and usability in a particular context • Constrained by a Service-Level Agreement (SLA)
Learning Package Overview1 Problem Description2 Using Data Properties in Quality Prediction3 Discussion4 Conclusions
Components Impacting Orchestration QoS Two groups of factors are usually encountered when analyzing QoS of a service composition: • External variations: Bandwidth, current load and throughput, network status Behavior of component services (e.g., meeting deadlines?) Usually not under designer’s control, they change dynamically • Composition structure: What does it do with incoming requests? Which other services are invoked and how? Partially under designer control, known in advance. Focusing on the latter, what kind of knowledge about composition behavior we can extract to predict composition QoS? Besides, can we make prediction more precise by taking into account characteristics of the data fed to the composition?
Automotive Scenario Example Suppose you are an car part provider hired by an factory to purchase a series of parts for its assembly line. • You are given a list of parts and their quantities • The parts must come from the same maker (be mutually compatible) • You contact a number of part makers and reserve each of the parts in the required quantity. • If a maker cannot provide all parts, you cancel all reserved parts from that maker and move to another maker. Maker 1 Factory Provider . . Maker K • Time is essential: you want the process to take the least amount of time and to include the smallest number of cancellations.
Automotive Scenario Example (contd.) In the service world, you publish to the Client (the factory) your Provider service that uses a series of Maker services. . eq rt r K Maker 1 Pa ot O n l K / ance O C Request Client Provider P OK ar t re / q Ca not O . nce K l Maker K • The protocol requires reserving one car part type at a time. If a maker answers with “not OK,” the provider sends “Cancel” messages for all reserved parts and starts reserving from another maker. The total time is linked to the computation cost of serving the client. • It depends heavily (among other things) on number of parts (in the input message) and characteristics of individual makers.
Computation Cost of Service NetworksComputation Cost Example TB1 (n) = n + 1 B1 TB1 (n) = n + 1 Input message abstracted as the the Input message abstracted as B1 to B 1? ing ? TA (n) = 2n + 3 + nS(n) A bind B 1 indin b b to g number of parts n. n. number of partsTA (n) = 2n + 3 + nS (n) A indin bin g to ding to B 2? B2 ? Time T for provider (A) depends Time TA forAprovider (A) depends TB (n) = 0.1n + B TB2 (n)2 = 0.1n + 7 7 2 B2 on n andand timetime)S(n) of the on n the the S (n of the chosen maker (B1 (B1Bor B2 ). chosen maker or 2 ). 140 QoS / Comp Cost for A+B1 QoS / Comp Cost for A+B2 Structural part part 2n in TAin TA does Structural 2n + 3 + 3 does not not depend the choice of maker. depend on on the choice of maker 120 QoS / Computational Cost 100 The graph shows the the QoS / The graph shows QoS / 80 computation costcosttwo possible computation for for two possible bindings: bindings: 60 TA withABwith) = 2n = 2n + (n + 1) + 1) T 1 (n B (n) + 3 + n3 + n(n 1 40 = n2 = n2 + 3n + 3 + 3n + 3 20 TA withABwith) = 2n = 2n + (0.1n + 7) + 7) T 2 (n B (n) + 3 + n3 + n(0.1n 4 5 6 7 8 9 10 2 Input data size (for a given metric) = 0.1n20.1n2 + 3 + 3 = + 9n + 9n Ivanovi´ et al. (UPM, IMDEA) c Data-Aware QoS-Driven Adaptation 2010-07-07 5
Computation Cost of Service Networks Computation cost information for B1 and B2 can be made available together with other service-related information (e.g., WSDL extensions): • Computation cost expressed as function of some metrics of input data. • Relationships between the size of input data and size of the output data (when they exist). A should in turn publish synthesized information (for reuse in other compositions involving A). Such abstract descriptions of computation cost do not compromise privacy of implementation details. • They act as higher-level contracts on composition behavior.ProblemInferring, representing and using the computation cost informationfor service compositions for QoS prediction.
Overview of the Approach Feedback Translation Analysis WSDL Trans la tion Intermediate Logic Analysis la tion language program results Trans BPEL Feedback 1 Service / orchestration descriptions represented in intermediate language. • Provides indepdence from the source language (BPEL, Windows Workﬂow, etc.) 2 Intermediate representation translated into (annotated) logic program. • Can capture just the relevant characteristics of the orchestration. 3 Logic program analyzed for computation cost bounds. 4 Analysis results useful for design-time quality prediction, predictive monitoring, matchmaking, etc.
Background: Alternatives in S-CubeOther S-Cube Approaches Include: Detecting Possible SLA Violations Using Data Mining • Extracting information from event logs of successful and failed executions of a composition in combination with event monitoring to identify critical points and inﬂuential factors that are used as predictors of possible SLA violations. Using Online Testing to Predict Fault Points in Compositions • Using model checking-based techniques on post-mortem traces of failed composition executions to identify activities that are likely to fail, both on the level of composition deﬁnition, and in particular cases of executing instances.
Beneﬁts of the Computation Cost Approach Statistical approaches: structure and environmental factors contribute to QoS variability: Environment factors Structural factors QoS • Hard to separate structural & environmental variations. • Whole range of input data may not be represented / sampled. • Runs may not be representative. • Results reﬂect historic variations in the environment. Structural approaches with data information: safe approximations of structural contributions. Environment factors Structural factor bounds QoS • Structural and environmental factors separately composed into QoS. • Entire input data range accounted for. • Results are safe and hold for all possible runs. • Results reﬂect current variations in the environment.
Computation Cost Analysis and SOA The computation cost approach relies on applying static cost analysis to service orchestrations: • Traditionally concerned with running time: Number of execution steps, worst-case execution time (WCET) • Generalized to counting and measuring events Number of iterations, number of partner service invocations, number of exchanged messages, network trafﬁc (number of bytes sent/received). Data Awareness: bounds expressed as functions of input data. • Magnitude of scalars: ﬂoating-point, ordinal and cardinal values • Measures of data structures: number of items in a list, depth of a tree, size of a collection Leveraging existing analysis tools. • In this case, for logic programs
Approximating Actual Behavior Bounds for Computation CostWith Upper and Lower Bounds Cost analysis (either automatic or manual) often can only determine safe Automatic analysis often cancomputation costs. upper and lower bounds. upper and lower bounds of only determine safe Exact cost function somewhere in somewhere in between. Exact computation cost function between. 140 Upper bound QoS / Comp Cost for A+B1 Lower bound QoS / Comp Cost for A+B1 Assumption: diﬀerent instances of Upper bound QoS / Comp Cost for A+B2 120 Lower bound QoS / Comp Cost for A+B2 Assumption: differentcontribute of the the same event type instances same event type contribute equally to equally to the overall computationQoS / Computational Cost 100 the overall computation cost. cost. 80 Safe computation are combinedare Safe cost bounds cost bounds 60 combined with current environment with current environment 40 parameters from monitoring (e.g., parameters from monitoring (e.g., 20 network speed) to produce QoS network speed) to produce QoS 4 5 6 7 8 9 10 Input data size (for a given metric) bounds. bounds. QoS ≈ cost ⊗ approximatednot combining cost bounds and environment QoS bounds environment by strictly safe, but: factors are not strictly safe, but: More informed than data-unaware, single point predictions, static •bounds, or averages. data-unaware, single point predictions, static More informed than Can be used averages. future behavior of a composition. bounds, or to predict • Can be used to predict future behavior of a composition. Ivanovi´ et al. (UPM, IMDEA) c Data-Aware QoS-Driven Adaptation 2010-07-07 7/1
Beneﬁts of Upper/Lower Bounds Approach QoS QoS Good for aggregate measures. F OCUS : Usually simpler AVERAGE to calculate. C ASE Not very informative for individual running Input data measure Input data measure instances. QoS QoS Can be combined with the average case F OCUS : approach. U PPER / More difﬁcult to L OWER calculate. B OUNDS Useful for monitoring / adapting individual Input data measure Input data measure running instances.I NSENSITIVE TO I NPUT DATA S ENSITIVE TO I NPUT DATA General idea: More information ⇒ more precision
Orchestration Intermediate LanguageIntermediate language (partly) inspired by common BPEL constructs:Data Types: XML-style data structures with basic (string, Boolean, number) and complex types (structures, lists, optionality).Expression language: XPath restricted to child/attribute navigation that can be resolved statically. Basic arithmetic/logical/string operations.Basic constructs: assignment, sequence, branching, and looping.Partner invocation: invoke follows the synchronous pattern. The moment of reply reception is not accounted for.Scopes and fault handlers: usual lexical scoping and exception processing.Parallel ﬂows: using logical link dependencies.
Translation into Logic Program Service: Translated into a logic predicate expressing a mapping from the input message to a reply or a fault. Invocation: Translated into a predicate call. Returns a reply or a fault. Assignment: Passes the expression value to subsequent predicate calls. Branching: Mutually exclusive clauses for the then and else parts. Looping: Recursive predicate with the base case that corresponds to the loop exit condition. Scopes: Sub-predicates for scope body and each deﬁned fault handler. Flows: Statically serialized according to logical link dependencies.Concrete Semantics and Resource Consumption Resulting logic program does not aim to mimic the operational semantics of, e.g., BPEL processes. Reﬂecting just the necessary semantics for resource analyzers to infer computation costs with minimal precision loss.
Obtaining Computation Cost Functions Example analysis of a simple scenario (one provider - one maker): part req. Request OK / not OK Client Provider Maker Cancel • not OK is treated as a fault by the provider. • two analysis variants: without fault handling (ideal case) and with fault handling (general case). As a generalized resource that is analyzed, here we take the number of Provider→Maker invocations for different n. • Can be related to the Key Performance Indicators (KPIs) Some events are related to business value for the provider and/or maker. E.g., minimizing cancellations (undesirable in general).
Example of Analysis Results Computation cost analysis results returned as upper and lower bound functions of n (number of parts to reserve). • These functions express the number of events: executions of simple activities in the orchestration reservations of single part type cancellations of previously reserved types • In the case without fault handling, we assume that each invocation is successful (i.e. the optimistic case). With fault handling Without fault handling Resource lower bound upper bound lower bound upper bound No. of simple activities 2 7n 5n + 2 5n + 2 Single reservations 0 n n n Cancellations 0 n−1 0 0
Application to Predictive Monitoring QoS metric Prediction after observation C Prediction after Max observation B Actual proﬁle Initially expected behavior History A B C D Notion of pending QoS – remaining metric until composition ﬁnishes. At point B, a deviation is detected from the initial prediction ⇒ it must come from environment. Updated prediction (densely dotted) for D still within range. At point C, further deviation detected. Updated prediction (loosely dotted) can fall out the range ⇒ violation of QoS concerns can be predicted ahead of time.
Experiment in Predictive Monitoring Simulation of a service-to-service call with time constraint Tmax : • Service A invoked with input message of size n in range 1..50 • A invokes service B between 50 and 100 times for n = 1, and between 250 and 500 times for n = 50 (the bounds are linear) • B performs between 8 and 16 steps on each invocation. • Each iteration of A and each step of B take some time between known bounds. Message and reply transfer times are environment factors. During execution of an orchestration instance for given n, the system takes into account: • known computation cost bounds (iterations, steps above) • the current environment factors and gives the following signals: • OK: time limit compliance guaranteed • Warn: time limit violation possible • Alarm: time limit violation certain The actual results are: OK for the time limit compliance and ¬OK for violation.
OK Warn/OK ,23 +23Experiment in Predictive Monitoring (Cont.) *23 23 + % . 0 *2 *+ *% *. *0 +2 ++ +% +. +0 ,2 Scenario 1: Environment factors suddenly double (on average) at * , - / 1 ** *, *- */ *1 +* +, +- +/ +1 456789: 45678;9: 6=89: 6= time Tmax /3 into execution of a composition!##$% instance. *223 *223 123 123 023 023 Warn/¬OK /23 Warn/¬OK /23 .23 .23 -23 -23 OK %23 ,23 OK Warn/OK Warn ,23 +23 /OK +23 %23 *23 Alarm/¬OK *23 23 23 + % . 0 *2 *+ *% *. *0 +2 ++ +% +. +0 ,2 ,+ ,% ,. ,0 %2 %+ %% %. %0 -2 % , . 0 *2 *% *, *. *0 %2 %% %, %. %0 + * , - / 1 ** *, *- */ *1 +* +, +- +/ +1 ,* ,, ,- ,/ ,1 %* %, %- %/ %1 * + - / 1 ** *+ *- */ *1 %* %+ %- %/ %1 456789: 45678;9: 6=89: 6=8;9: ;6=89: ;6=8;9: 456789: 45678;9: 6=89: 6= Fig. 6. Ratio of true and!##$% • For small n, violations are not predicted and dopositives for two environmenta false not happen (OK) • For slightly larger n, some false warnings arise (Warn/OK) Under the ﬁrst regime, composition executions for small va *223 • For large n, false warnings yield to true violation warnings (Warn/¬OK) 123 time to complete, so they comply with the time limit (marked b 023 Warn/¬OK and true alarms (Alarm/¬OK) /23 are raised. For slightly larger input sizes (e.g. n = 9), executions s .23 • There are no false OKalarms (Alarm/OK). time limit, but warnings are raised (Warn/OK), since the moni -23 Alarm/¬OK ,23 Warn Conclusion: very good prediction accuracy, with max . As n increases, the num upper bound running time exceeds T some false warnings +23 /OK positives decreases in favor of the true warning positives (Warn/ %23 in the lower mid-range of n. *23 average running time increases and thus the possibility of execu 23 % , . 0 *2 *% *, *. *0 %2 %% %, %. %0 +2 +% +, +. +0 ,2 ,% ,, ,. ,0 -2 by sudden deterioration of the environment factors. In the same * + - / 1 ** *+ *- */ *1 %* %+ %- %/ %1 +* ++ +- +/ +1 ,* ,+ ,- ,/ ,1
,23 +23 Experiment in Predictive Monitoring (Cont.) Alarm/¬OK *23 23 + % . 0 *2 *+ *% *. *0 +2 ++ +% +. +0 ,2 ,+ ,% ,. ,0 %2 %+ %% %. %0 -2 Scenario 2: Environment factors gradually deteriorate (quadrupling * , - / 1 ** *, *- */ *1 +* +, +- +/ +1 ,* ,, ,- ,/ ,1 %* %, %- %/ %1 456789: 45678;9: 6=89: 6=8;9: ;6=89: ;6=8;9: on average) during the period Tmax from the start of execution. !##$% !##$% *223 123 023 Warn/¬OK Warn/¬OK /23 .23 -23 OK Alarm/¬OK ,23rn/OK Warn +23 /OK %23 Alarm/¬OK *23 23*% *. *0 +2 ++ +% +. +0 ,2 ,+ ,% ,. ,0 %2 %+ %% %. %0 -2 % , . 0 *2 *% *, *. *0 %2 %% %, %. %0 +2 +% +, +. +0 ,2 ,% ,, ,. ,0 -2, *- */ *1 +* +, +- +/ +1 ,* ,, ,- ,/ ,1 %* %, %- %/ %1 * + - / 1 ** *+ *- */ *1 %* %+ %- %/ %1 +* ++ +- +/ +1 ,* ,+ ,- ,/ ,178;9: 6=89: 6=8;9: ;6=89: ;6=8;9: 456789: 45678;9: 6=89: 6=8;9: ;6=89: ;6=8;9:6. Ratio of true and!##$% positives for two environmental regimes. false • For small n, do not happen (OK), but there are some false warnings (Warn/OK) ﬁrst regime, composition executions for small values of n take little • For larger n, false warnings yield to true violation warningsete, so they comply with the time limit (marked by OK) and no alerts arn/¬OK slightly larger(Warn/sizes (e.g. ntrue alarms (Alarm/¬comply with the input ¬OK) and = 9), executions still OK) • Alarm/¬OK are again no false alarms (Alarm/OK) There (Warn/OK), since the monitor’s estimate of the warnings are raisedunning time exceeds Twhen conditions gradually deteriorate, the prediction Conclusion: max . As n increases, the number of false warningeases in favor of the true warning positives (Warn/¬OK), because the tends to become more accurate on average.ng time increases and thus the possibility of execution being affected *, *. *0 %2 %% %, %. %0 +2 +% +, +. +0 ,2 ,% ,, ,. ,0 -2 (#)*erioration of the environment factors. In the same region (around n =*+ *- */ *1 %* %+ %- %/ %1 +* ++ +- +/ +1 ,* ,+ ,- ,/ ,1
Experiment in Proactive Adaptation Tier 1 Tier 2 Client chooses provider Pj from P1 S1 ub1 (n) UB 1 (m) ﬁrst tier of services, passing the P2 S2 ub2 (n) input argument m = 0..50. UB 2 (m) . .Client . . . . Chosen provider chooses M = 5 PN SN ubN (n) times a part maker (the second UB N (m) tier) with the input n = m.250 ub_1(x) ub_2(x) ub_3(x) Plot depicts family of upper bound ub_4(x)200 ub_5(x) ub_6(x) ub_7(x) functions for structural computation ub_8(x) ub_9(x) ub_10(x) ub_11(x) cost for the ﬁrst and the second tier. ub_12(x) lub(x)150 Structural computation cost models100 number of messages exchanged (without messages between the 50 tiers). 0 0 10 20 30 40 50 Fault rate used to model service unavailability.
Experiment in Proactive Adaptation (Cont.) Tier 1 Tier 2 P1 S1 ub1 (n) Selection of ﬁrst/second tier UB 1 (m) service done using: P2 S2 ub2 (n) UB 2 (m) . • random choice; . . .Client . . • ﬁxed preference (lowest PN SN ubN (n) computation cost for n = 12); and UB N (m) • data-aware computation cost250 minimization ub_1(x) ub_2(x) ub_3(x) ub_4(x)200 ub_5(x) ub_6(x) ub_7(x) Message passing times for the ub_8(x) ub_9(x) ub_10(x) ub_11(x) services simulated using the ub_12(x)150 lub(x) following two regimes:100 (A) Random Gaussian choice with average 5ms for all services. 50 (B) Varying average 4-8ms. 0 0 10 20 30 40 50 Effectiveness of policies compared w.r.t. total simulated time.
A Simulation Experiment (Cont.) Simulation results indicate that for both cases (A and B) of service running time variations, the data aware outperforms both the random choice and ﬁxed preference policies. • x-axis gives input data size in the range 0-50 • y-axis gives total simulated running time • The fault rate is pf = 0.001 Time [ms] Time [ms]6000 6000 random random fixed fixed data data5000 50004000 40003000 30002000 20001000 1000 sim_s1_pf001.data sim_s2_pf001.data 0 0 5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50
Experiment in Proactive Adaptation (4) Another set of simulation results for pf = 0.1 (below) indicate that the advantages of using the data aware service selection policy persist even under very high noise / failure / unavailability rates. • included both cases (A and B) of service running time variations • overall, the data awareness gives best results for very small and big input data sizes Time [ms] Time [ms]6000 6000 random random fixed fixed data data5000 50004000 40003000 30002000 20001000 1000 sim_s1_pf100.data sim_s2_pf100.data 0 0 5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50
Current Restrictions on Orchestrations Currently, we are looking at “common” orchestrations that respect some restrictions w.r.t. behavior. • Overcoming these limitations is a goal for future work. Orchestrations must follow receive-reply interaction pattern: • All processing between reception of the initiating message and dispatching of (ﬁnal) response. • Applicable to processes that accept one among several possible input messages. • Future work: relax restriction by using fragmentation to identify/separate reply-response service sections. Orchestration must have no stateful callbacks: • I.e., no correlation sets / WS-Addressing. • Practical problem: current analyzers lose precision when passing opaque objects containing state. • Future work: improve translation and analysis itself.
Conclusions Data-aware computation cost functions can be used to predict QoS and thus drive QoS-aware adaptation or signal certain or possible QoS violations. Based on a translation scheme that, from an orchestration represented in an intermediate language, a logic program is generated and analyzed by existing tools. • Analysis derives computation cost functions which are safe upper and lower bounds of the orchestration’s computation cost. • The computation cost functions are expressed as functions of the size of input data, expressed in some appropriate data metrics. • Computation cost functions are combined with environment factors used to build more precise QoS bounds estimations as a function of input data.
Conclusions (Cont.) In predictive monitoring, simulation results suggest high accuracy of predictions ahead of time, including situations when environmental conditions gradually deteriorate. • The time before detection and occurrence of a violation may be used for preparing and triggering the appropriate adaptive action. Simulation results indicate the usefulness of the approach in improving the efﬁciency of dynamic, run-time adaptation based on QoS-aware service selection. • In general, data-aware adaptation gives better results than other service selection policies — even with very large variability in service availability. The idea is to integrate the presented approach into service composition provision systems, collect empirical data and compare and combine it with statistical / data mining approaches.
References This presentation is based on [ICH10a, ICH10b]. Some pointers on QoS analysis and prediction for Web service compositions: [Car05, Car07, LWR+ 09, HKMP08, DMK10] Some pointers on automatic complexity analysis / computational cost / resource consumption analysis: [HBC+ 12, HPBLG05, NMLH09, NMLGH08, ABG+ 11]
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Acknowledgments The research leading to these results has received funding from the European Community’s Seventh Framework Programme [FP7/2007-2013] under grant agreement 215483 (S-Cube).
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