1. 1 Pierre Deransart WLPE 061 On Using Tracer Driver for External Dynamic Process Observation Pierre Deransart WLPE 2006

2. 2 Pierre Deransart WLPE 062 Loria Rocquencourt Sophia Antipolis Irisa Rhône-Alpes Futurs Les unités de recherche

3. 3 Pierre Deransart WLPE 063 BASIC MOTIVATIONS Dynamic Program Analysis: typical recent works are based on trace analysis Ernst & al. 2001: “Dynamically discovering likely program invariants…” from data computed by dynamic execution Denmat & al. 2005 “Data mining and Cross-checking of Execution Traces…” from a collection of traces Zaidman & al. 2005 “Applying Webmining Techniques to Execution Traces…”

4. 4 Pierre Deransart WLPE 064 WHY TRACES ? Any phenomenon, any open system leaves traces Walking (persistent foot traces) Sedimentation (temporally accumulated traces), fossils Particles (light): objects only known by their physical or chemical properties Programs (outputs, observation) Communication (messages) Discourse abstract Human Memory…(persistent and reactive) Traces are everywhere: we only know processes by their traces

5. 5 Pierre Deransart WLPE 065 OBSERVING PROCESSES Everybody watches everyones….. Everybody receives from everyone Everybody sends messages to …

6. 6 Pierre Deransart WLPE 066 « Leave traces, not proofs, only traces give dreams » René Char Poète (1907-1988)

7. 7 Pierre Deransart WLPE 067 We know and define complex objects from the traces they leave We know complex programs behaviour by analyzing their traces Causal analysis is not tractable  likely causality TRACE modeling is the right approach

8. 8 Pierre Deransart WLPE 068 BUT, what IS a TRACE ??? HOW to ANALYSE IT ??? I want to leave these questions open ….small demo

9. 9 Pierre Deransart WLPE 069 What IS a TRACE ??? the answer is: Any possible understandable information related to an observed phenomenon PRO Any observing device will find in the trace what it needs If a process needs instrumentation to produce a trace, this need only to be made once Analysis tools may be developed independently

10. 10 Pierre Deransart WLPE 0610 CON: - it is not possible to broadcast such a huge information flow (communication slowing down) - then the observed process always computes a huge amount of unused data (construction slowing down)

11. 11 Pierre Deransart WLPE 0611 SPECIFIC ASPECTS Needs for trace standardization All levels of granularity accepted Different kinds of informations included (levels of abstraction) Each analyser must be able to recognize its relevant information Use of XML to define possible standards

12. 12 Pierre Deransart WLPE 0612 SEEMS an UNREALISTIC GOAL !!! the answer is: Driven Tracer SPECS selects in the trace what the observer needs keeps tracer listening to the analyzers (dialog between server and clients) Leave the tracer to distribute and broadcast each specific trace Allow workload repartition between tracer and analysers

13. 13 Pierre Deransart WLPE 0613 ORGANISATION History Virtual Full Trace Processes organization Workload analysis Driver requirements Conclusions

14. 14 Pierre Deransart WLPE 0614 HISTORY Ducassé, Opium: versatile analyzers Ducassé, Noyer, 1994, JLP: independence of tracer and analyzers Langevine & Ducassé & Deransart, 2003, ICLP’03: Codeine, First Driven Tracer approach implementation for GNU-prolog Deransart & all, 2004, OADymPaC project: client/server architecture, trace standardization (XML) for interoperability Langevine & Deransart & Ducassé, 2004, LNAI 3010: model of « generic trace » for constraint programming Langevine & Ducassé, 2005, AADEBUG, WLPE: Driven Tracer for FD constraints and experimentation Now, 2006: « theory » of generic trace and driven tracer = virtual full trace

15. 15 Pierre Deransart WLPE 0615 VIRTUAL FULL TRACE (definition) unbounded sequence of trace events of the form e t : (t, a t, S t+1 ) e t : unique identifier of the event t: chrono. Time of the trace S t = p 1,t..., p n,t : parameters at chrono t. In a trace event the parameters are called attributes and S t the full current state a t : action characterizing the step of the state S t to the state S t+1. It can be described by a set of transformations which describes the operations carried out on the current state

16. 16 Pierre Deransart WLPE 0616 EFFECTIVE TRACE a full trace of the form e t : (t, A t ) such that, starting from the knowledge of (S t,A t ) one can deduce (a t, S t+1 ). A t denotes a set of attributes. The effective trace is the trace emitted by a tracer, which is actually ``visible''. The virtual full trace is a particular case of effective trace where the attributes A t are the actions a t and the parameters S t.

17. 17 Pierre Deransart WLPE 0617 EXAMPLE (effective trace) 1 1 Call: '$call$'(bench(2)) 2 2 Call: bench(2) 3 3 Call: 2>0 3 3 Exit: 2>0 4 3 Call: _182 is 2-1 4 3 Exit: 1 is 2-1 5 3 Call: bench(1)....

18. 18 Pierre Deransart WLPE 0618 INCREMENTAL TRACE the attributes are such that only the changes affecting the current state are noted. e t : (t, Delta t +) where Delta t + contains the description of the actions which modify the values of the parameters at moment t. To remain a full trace, this trace must satisfy the following condition: For every t (t, a t, S t+1 ) can be deduced from (S t, Delta t +)

19. 19 Pierre Deransart WLPE 0619 CLIENT/SERVER architecture

20. 20 Pierre Deransart WLPE 0620 CLIENTS/server architecture

21. 21 Pierre Deransart WLPE 0621 CLIENTS / server architecture Workloads are distributed among Program (without connections with tracer) T_prog Tracer (parameters and attributes computation) T_core + T_extract Driver (dialog and attributes selection) T_cond Broadcasting (all traces encoding) T_encode-and-com ==================================================== Reception (dialog and post-selection) T_filter Trace decoding T_decode Trace rebuilding T_rebuild Analyzer execution T_ana

22. 22 Pierre Deransart WLPE 0622 CLIENTS / server architecture Process --------------- | T_prog + T_core1 Tracer and Driver ----------------------------------------------- | T_core2 + T_cond + T_extract + T_encode-and-com ========================================================= Analyzer ------------------------------------------ | T_filter + T_decode + T_rebuild + T_ana

23. 23 Pierre Deransart WLPE 0623 Workload balance Process and Tracer --------------- | T_prog + T_core Analyzer --------- | | T_ana Analyzer --------- | | T_filter Driver --------- | T_cond Tracer --------- | T_extract Analyzer --------- | | T_rebuild Tracer ----------------- | T_ encode-et-com Analyzer --------- | T_decode ====================================================================================================

24. 24 Pierre Deransart WLPE 0624 OBSERVATIONAL SEMANTICS Two levels Objects level: read the trace (parameters and attributes description and relationships) Trace steps level: understand underlying model (full state transformations) It may be a rule semantics (finite number of rules) a: Condition(S)  S’ := a(S)

25. 25 Pierre Deransart WLPE 0625 OBSERVATIONAL SEMANTICS The OS is usually not a complete operational semantics Knowing S_t and S_t+1, one rule applies but the knowledge of S_t is not always sufficient to know which rules can be applied (to be studied) Not all attributes can be formalized in the OS (one should have a full model of the observed process) There may be as many OS than observers

26. 26 Pierre Deransart WLPE 0626 DRIVER REQUIREMENTS In addition to the tracer’s work, it must Analyze trace queries Store and manage requested trace patterns Manage the dialog between server (tracer) and clients (analyzers) Tell the tracer what to extract and to broadcast

27. 27 Pierre Deransart WLPE 0627 GENERAL CONCLUSION : Possibility to implement very large virtual full trace without slowing down excessively the observed process More sophisticated analyses will be performed, larger can be the virtual full trace Trace selection and filtering can be very efficient using a tracer driver Effective trace size can be reduced by different means: compression (delta and classical compression) or abstraction (transfer more complex objects)

28. 28 Pierre Deransart WLPE 0628 QUESTIONS Is a « never more » - extensible full virtual trace possible? How to parameterize the compression (to specify the level of abstraction of communicated objects)? Full virtual trace standardization (work on constraint problems), how? XML effort? OS discovery from trace (trace mining), assuming trace objects are known? Consider other fields where the notion of trace is relevant? TRA4CP project

29. 29 Pierre Deransart WLPE 0629 Thank you!