Business-Driven Software Engineering (12. Vorlesung) Translation, Performance Considerations Thomas Gschwind <thg at zurich.ibm.

Transcription

1 Business-Driven Software Engineering (12. Vorlesung) Translation, Performance Considerations Thomas Gschwind <thg at zurich.ibm.com> Thomas Gschwind

2 Agenda BPMN Translation Running sample State of the Art Implementing a simple BPMN Compiler Performance Considerations Fallacies and pitfalls Clustering Timer Services Exercise Questions

3 The Mortgage Application Process Demonstrates a simple business process Even in that simple process, not every implementation aspect is interesting on the BPMN level This half of the business process is modeled extensively

4 The Mortgage Application Process (cont d) This side omits certain data items in the business process On the rejection path, all data objects are omitted This has been done for clarity reasons This part was considered straight forward

5 State of the Art Compilation/Execution Compile Business Process into executable code Today, BPEL is used as executable code BPEL development tools look and feel like advanced BPMN Direct Execution of BPMN Assumes that all information is provided at the BPMN level Not every problem can be efficiently implemented with BPMN

6 BPEL Sample <bpws:process name="proxyprocess" suppressjoinfailure="yes" targetnamespace=" wpc:id="1"> <bpws:partnerlinks> <bpws:partnerlink myrole="oracleinterfacerole" name="oracleinterface" partnerlinktype="ns:oracleinterfaceplt"/> <bpws:partnerlink name="echointerfacepartner" partnerlinktype="ns:echointerfacelt" partnerrole="echointerfacerole"/> </bpws:partnerlinks> <bpws:variables> <bpws:variable name="input1" type="xsd:string" wpc:id="2"/> <bpws:variable name="output1" type="xsd:string" wpc:id="3"/> </bpws:variables> <bpws:sequence name="hiddensequence" wpc:id=" "> <bpws:receive createinstance="yes" name="receive" operation="asktheoracle" partnerlink="ora <wpc:output> <wpc:parameter name="input1" variable="input1"/> </wpc:output> </bpws:receive> <bpws:invoke name="invoke" operation="echooperation" partnerlink="echointerfacepartner" por <wpc:input> <wpc:parameter name="message" variable="input1"/> </wpc:input> <wpc:output> <wpc:parameter name="result" variable="output1"/> </wpc:output> </bpws:invoke> <bpws:reply name="reply" operation="asktheoracle" partnerlink="oracleinterface" porttype="n <wpc:input> <wpc:parameter name="output1" variable="output1"/> </wpc:input> </bpws:reply> </bpws:sequence> </bpws:process>

7 BPMN Process to BPEL BPMN Business Process compile BPEL Implementation refine Maintains two different models that need to be translated between Software engineers are expected to extend the generated BPEL code BPEL is a verbose XML based language Can be manipulated visually with tools Problem if original BPMN process is changed Problem if changes in the BPEL code are necessary that should be propagated back to BPMN Creates artificial versioning problems Worse if changes in the BPEL code that should not be propagated back since on a conceptual level the BPMN process is correct

8 Direct Execution of BPMN Will solve the problems only partially Why? BPMN and BPEL intended for execution in the large Cannot deal well with lower level implementation artifacts Typically, this is solved by invoking web services to perform the actual tasks Not all low-level artifacts can be integrated as a service Returning a database connection from a service is hard Using a web service for sorting a small number of elements is not ideal Not every Business Analyst supports the execution of BPMN Phil Gilbert, Vice President BPM, IBM The BPMN standards effort has lost its way Today's methods / implementations do not allow Business Processes to be implemented efficiently

9 BPMN Translation: Overview Follows the Model-Driven Software Development approach Translate process into traditional language as abstract class Implementation overrides abstract methods, may use other libraries Compile with the language compiler Business Process Abstract Process Class extends Ensures implementation of all artifacts Identify activities being added or changed Verifies whether implementation fulfills contracts defined in original business process Tracks functions with a changed signatures tool generated UML Diagrams Data Classes Process Implementation javac Executable Libraries uses

10 BPMN Translation: Code Generation Implementation uses Java as implementation language Generate abstract methods for the individual activities: abstract void ComputeRequiredFunds(Application application) abstract void ComputeAvailableFunds(Customer customer) Similarly generate abstract methods for the conditions Implementation provided by extending the above Java class Allows compiler to identify new and renamed methods Generate a method that represents the flow Maps the flow between the activities Invokes the abstract methods

11 BPMN Translation: Workflow Convert into a state machine Workflows do not tend themselves easily to structured programs Find a way to convert a process into more structured fragments Use an abstraction of the original workflow referred to as Process Structure Tree Based on the notion of SESE fragments A SESE fragment is a fragment with a single-entry and a single-exit Can be computed automatically in linear time

12 Process Structure Tree Z f7 X J d1 C f1 A B a1 a2 j1 m1 K f2 E a4 f3 G a6 j2 I a8 j3 L a9 j6 D a3 F a5 H a7 Y V d2 O f4 M N m2 j4 a10 a11 P a12 m3 Q a13 d3 W d4 f5 f6 R S a14 a15 m4 m5 T U a16 a17 j5 Z f7 X Y j6 J K L V W d1 C D m1 f2 E F f3 G j2 H I j3 a9 d2 O m2 P m3 Q d3 d4 f5 R f6 S m4 T m5 U j5 f1 A B j1 a3 a4 a5 a6 a7 a8 f4 M N j4 a12 a13 a14 a15 a16 a17 a1 a2 a10 a11

13 Types of Fragments Sequence Convert into sequence of statements Parallel Fragment Convert into if ( ) { } else if ( ) { } Create multiple threads, run them, and join them at the end Loop Convert into do { } while ( ) Convert into while ( ) { } Convert into a hybrid version thereof Unstructured Fragments Convert into a state machine

14 BPMN Translation: Data Objects The Business Process specifies data items Connect data items to UML diagrams Can be defined within the business process Can be defined separately using a data-binding definition

15 Agenda BPMN Translation Running sample State of the Art Implementing a simple BPMN Compiler Performance Considerations Fallacies and pitfalls Clustering Timer Services Exercise Questions

16 Word of Caution There is not one way to do something right This lecture cannot tell you what to do This lecture only tells you what to look for BUT Many ways exist to do something wrong! What are the advantages of each approach? What are your requirements? Think!

17 Performance Issues Define the performance requirements from the start Tuning an application involves several layers OS, JVM, database, application server, etc. Be careful with memory resources Make sure to release objects that are no longer needed Generally, stick to the conventions Session Beans, session management Entities, data

18 Session Beans: Stateful versus Stateless Stateful beans State is lost if bean crashes Good if multiple invocations required Bean needs to be aware of transactions Should be released by clients if no longer needed Stateless beans May be pooled easily Send client state for each call Store state persistently Require client to pass session id Easier to convert to a Web Service

19 Message-Driven Beans: When to Use? Tradeoffs Performance (async. invocation) Reliability Support multiple senders & receivers JMS Advantages Load balancing Request priorization Good for loosely coupled systems (e.g., WAN) RMI-IIOP Advantages Good if program has to be notified when request is done Return result Can participate in client-transactions Security Error detection (Strong typing)

20 Remote Invocations: Latency Be careful of the latency of remote invocations Avoid many invocations that return only little data If your invocations are too fine grained, use a method that aggregates multiple requests This was one of the problems of pre-ejb3.0 Entity Beans Avoid exposing them to remote clients One request per required attribute One transaction per attribute Use a session bean that returns data using call-by-value which returns all data at once in a single request with a single transaction

21 Performance Tuning Use local interfaces when possible Transactions Keep transactions short Isolation levels Use caching Use CMP instead of BMP (less SQL requests) Use lazy loading if you do not use entire bean s data

22 Pooling of EJBs Stateful Session Beans Tune pool size Tune caching Control serialization Stateless Session Beans Tune pool size Efficient resource caching Message-Driven Beans Tune pool size

23 Tips and Tricks Try to match your database and object model Easy when system developed from scratch Harder if legacy system is extended Normalized versus denormalized database Denormalized may be db more performant Harder to understand Use as last resort!

24 Tips and Tricks (cont d) Keys Using natural key simplifies key managed Problems if natural key changes Use surrogate key instead Caution: Introducing an artificial can yield redundancies, use database constraints

25 Tips and Tricks (cont d) Living with Legacy Databases (Good Luck!) Single column used for different purposes Map to multiple EJB attributes Use legacy design Purpose of column is defined by other value Probably use BMP Incorrect data values CMP that verifies data in ejbload() Multiple sources for data BMP that uses preferred source, warn about inconsistencies Entities floating in text fields Parse information, you will have to live with minor problems

26 Large-Scale System Large-scale system requires the application server to be clustered Terminology Reliability Availability Serviceability Think of the growth of your system right away

27 Clustering Load-balancing performed by web or application server JNDI Driver Container Stubs (pre-ejb3.0, either Home Stub or Remote Stub)

28 Clustering Pure load balancing does not deal with failures Dealing with failures Request-level fail over Session-level fail over Requires replicated servers

29 Idempotence Independently of how often a method is being invoked it has the same effect as if it was only invoked once

30 Stateless Session Bean Clustering Load Balancing No state => may always call a different bean Fail-over ejbcreate() fine Remote methods only if they are idempotent

31 Stateful Session Bean Clustering Typically a primary bean is created Serves all client requests State replicated to other servers At the end of methods At the end of transaction Coarse grain load balancing Backup only contacted if primary copy fails (external resources) Fail-over Between method-calls (idempotent methods may be restarted) Between transactions

32 Entity Bean Clustering Load Balancing Contacted only by session beans Contacted only through local interface Load balanced as a consequence of session bean Fail-over No, only in combination with session bean Otherwise, fail-over from local to remote interface

33 Message Driven Bean Clustering Load balancing Pull themselves messages when ready Works fine with queues Fail-over Problems handling the message? Don t acknowledge until done Be careful to undo data Be careful to live with partially executed message handlers

34 Other Clustering Issues Use JNDI service to look up data Centralized JNDI service may fail Shared/replicated Each node has a name server Contains replicated objects on other servers Replicates those servers contents Initial Access Logic Round Robin DNS Software Proxies Hardware Proxies

35 Agenda BPMN Translation Running sample State of the Art Implementing a simple BPMN Compiler Performance Considerations Fallacies and pitfalls Clustering Timer Services Exercise Questions

36 The EJB Timer Service Many systems provide such a service UNIX: cron, at, etc. java.util.timer API Until EJB 2.0 no timer support Quartz Sims Computing Flux Scheduler

37 Obtaining the Timer Service Timer Service 2. call() 1. register() Enterprise Bean For any bean (except stateful session beans) Entity bean => Associated with concrete entity Timer registration & cancelation part of transaction

38 The Timer Service API Use Context to get hold of it {Session,Entity,MessageDriven}Context ctx; ctx.gettimerservice(); Implement TimedObject interface public interface TimedObject { public void ejbtimeout(timer timer); }

39 Timer Service Methods createtimer( ) One-time notification at time t One-time notification after t millis Recurrent notification every t millis starting at time t Recurrent notification every t millis starting in t millis gettimer( ) Obtain a list of currently active timers

40 Strength & Limitations Why a new service Could be implemented externally Limited Configuration Options Likely to change in next version of spec. Not much flexibility in the scheduler

41 Agenda BPMN Translation Running sample State of the Art Implementing a simple BPMN Compiler Performance Considerations Fallacies and pitfalls Clustering Timer Services Exercise Discussions

42 EJB Exercise Questions: Use Case Implementation of use cases? Implement a set of test cases to test your bank service Implement a command line client (or multiple) that allows to invoke different operations Please prepare a presentation of the exercise and make sure that the CLI allows to show things nicely The command line client should also be able to create specific new customers, accounts, etc. Web interface is not necessary but if available will be considered positively for the final grade of the exercise Can compensate small mistakes in different component Cannot compensate for an entirely missing component (e.g., security)

43 EJB Exercise Questions: Transactions I Switching isolation level of the database Not necessary but for experimentation, can be done on database or with application server specific configuration files For JBoss, use SET DATABASE DEFAULT ISOLATION LEVEL { READ COMMITTED SERIALIZABLE } Deadlocks? Two transactions (transfer(1,2,30) && transfer(2,1,50)) in parallel Depending on isolation level, one will fail or database will deadlock Deadlock is identified by database and will be resolved by database (e.g., rolling back one of the transactions) Customer exceeds credit limit? Mark transaction as rollback-only? Identify early and avoid having to mark transaction as rollback-only?

44 EJB Exercise Questions: Transactions II If customer exceeds credit limit, mark transaction as rollback-only Why? Let s consider we want to identify it, where should the check be placed? Scope of the caller? What if the code is invoked from different places? Potentially massive code duplication! Code duplication can grow exponentially if there are more such checks! Within the method that performs the function? Simply ignore the transfer? What happens if the withdraw function is executed from another method (e.g., buy_stock)? Reuse the mechanism that is there and DON T reinvent a mechanism that is already there!

45 EJB Exercise Questions: Transactions III No effect of transactions Client contains transfer(1,2,30); transfer(1,3,30); The two methods are always executed independently of each other independently of whether we use Requires or RequiresNew For each method consider whether it can be used as part of another method on the server-side (e.g., buy_stock)! Whenever a method changes, re-evaluate its transaction attributes and those of the methods being invoked!

46 EJB Exercise Questions: Security Mapping of roles in deployment descriptor? Not necessary, don t worry about it Problems with changing username and password? Remove and redeploy the beans Potentially restart JBoss Alternatively use a database-based authentication module

47 Summary BPMN Translation Running sample State of the Art Implementing a simple BPMN Compiler Performance Considerations Fallacies and pitfalls Clustering Timer Services Exercise Discussions

48 Review Questions How to convert a given workflow to Java code When to use Stateful or Stateless Session beans or Message-Driven Beans Active vs. lazy loading of entity beans What is an idempotent operation Clustering of Session Beans 48

49 EJB Exercise Part II Client side: Implement a client that allows a user to invoke the different functions provided by the server-side beans Implement a set of test cases that verifies your implementation Processes: Implement the Mortgage Business Process Analyze whether the process is better be implemented on the client or server side Server side: Implement portfolio items (stock symbol, quantity, account number) Allow to transfer stocks The function takes the account# of a seller and a buyer, the number of stocks to be bought, and a price Yes, in theory we would also need a marketplace but this is left for another lecture

50 Outlook Pre-EJB 3.0 Beans 50