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Transaction Management

Jul 28, 2014 19:51

George Hoffer

Sep 12, 2014 12:28

Mulesoft Current Mule Documentation

Transaction Management

Mulesoft Documentation Page

Contents

Transaction Management

 Contents

Mule applies the concept of transactions to operations in application for which the result cannot remain indeterminate.  In other words, where a series of steps in a flow must succeed or fail as one unit, Mule uses a transaction to demarcate such a unit.  For example, you might use a transaction to encapsulate several steps in a flow for which the end result involves committing information to a database.  In this type of scenario, the commit is either entirely complete and succeeds, or is incomplete and it fails. Even if partially complete, the commit – or transaction – fails. Where a transaction fails, Mule rolls back the operations within the transaction so that no one part results in partial completion.

You can demarcate a transaction by applying a transaction to a connector. If a Mule flow begins with a transactional resource (such as an inbound connector), Mule can start a new transaction and manage the entire flow as a transaction. If your flow includes a transactional outbound connector, Mule manages the outgoing operation as a transaction. With both a transactional inbound and outbound connector, Mule executes the outgoing operation as part of the transaction initiated by the inbound connector.

The following connectors support transactional demarcation:

  • JMS
  • JDBC
  • VM

Note: As of Mule 3.5.0, the Database Connector replaces the JDBC connector, and the JDBC connector is deprecated. Applications that use the JDBC transport continue to work with the 3.5.0 Enterprise Runtime, but the connector is no longer available in the Studio palette to add to applications.

A Mule flow may begin with a non-transactional inbound connector – such as HTTP or SFTP – but which requires the use of a transaction within the flow. For example, a Mule flow may accept information from an external Web service,  then transform the data, before charging a credit card, and saving invoice information to a database. In such a situation, you can demarcate a transaction by wrapping the credit card charge and database commit operations within a transaction to ensure either complete success or complete failure and rollback.

Transaction Types

Mule supports three different types of transactions: single resource, multiple resource, and extended architecture (XA). The following table describes characteristics of each type.

Note: JDBC is deprecated.

TypeCharacteristicsNumber of ResourcesAvailable ResourcesPerformance
Single Resource Transactions
  • Receives or sends messages to only one resource.
1
  • JMS
  • VM
  • JDBC 
  • Relative to the others, performs better
Multiple Resource Transactions
  • Receives or sends messages to more than one resource.
  • Can handle partial commits and rollbacks. 
  • Uses 1.5 commit protocol as opposed to two-phase commit protocol.
>1
  • JMS
  • VM
  • JDBC
  • Performs better than XA, though slower than Single Resource
  • With 1.5PC, functions less reliably than XA.
XA Transactions
  • Receives or sends messages to more than one resource.
  • Involves using an two-phase commit algorithm
  • Connectors must be XA-enabled.
>1
 
  • JMS
  • VM
  • JDBC 
  • Relative to the others, performs slower but more reliably
Multi-source vs. XA

While XA Transactions offer similar functionality, Multiple Resource transactions use less overhead.  XA transactions are more reliable. Both can include JDBC resources. For a discussion of different approaches – including the 1.5 phase commit concept which Multiple Resource transactions use – see the JavaWorld article on distributed transactions.

 

Assumption

This document assumes that you are familiar with Mule ESB and/or the Anypoint Studio interface. To increase your familiarity with Anypoint Studio, consider completing one or more Anypoint Studio Tutorials. Further, this document assumes you have some knowledge of transaction processing and are familiar with Anypoint Connectors.  

 

Configuring Transactions

You can demarcate a transaction by either applying a transactional configuration to a connector, or by wrapping several elements in a transactional wrapper.

  • Apply a transaction to an inbound connector when you want Mule to handle the complete flow as a transaction.
  • Apply a transaction to an outbound connector when you want Mule to handle the outgoing operation as part of an existing transaction.
  • Apply a transaction as a wrapper (known as a scope in Studio) when you want to apply a transaction to elements within a flow that do not begin with a inbound connector configured as a transaction.

 The following subsections outline the steps to apply transactions in your flow.

Applying a Transaction to a Connector

You can apply a transaction to any of the following inbound or outbound connectors:

  • JMS
  • VM
  • JDBC (Deprecated)
    1. In the connector's properties editor, click the General tab to access the Transaction pane (see image below of the JMS connector).



    2. Configure the transactional attributes according to the tables below.

      AttributeValueAvailable on ConnectorUse
      Type




      JMS TransactionJMSApply a transaction to a flow that involves a single resource (simple).
      JDBC TransactionJDBCApply a transaction to a flow that involves a single resource (simple).
      VM TransactionVMApply a transaction to a flow that involves a single resource (simple).
      XA TransactionJMS VM JDBCApply a transaction to a flow that involves multiple resources.
      Client Ack TransactionJMSApply a transaction to a flow that involves multiple resources.
      Multi-resource TransactionJMS VM JDBCApply a transaction to a flow that involves multiple resources.
      Action




      NONEJMS VM JDBCWhen it receives a message, Mule resolves the transaction, then executes the operation as non-transactional.
      ALWAYS_BEGINJMS VM JDBCWhen it receives a message, Mule always starts a new transaction.
      BEGIN_OR_JOINJMS VM JDBCWhen it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.
      ALWAYS_JOINJMS   VM JDBCWhen it receives a message, Mule always expects a transaction to be in progress, and always joins the transaction. If no transaction is in progress, Mule throws an exception.
      JOIN_IF_POSSIBLEJMS   VM JDBCDefault When it receives a message, Mule joins the current transaction if one is available. Otherwise, Mule does not begin a transaction.
      NOT_SUPPORTEDJMS VM JDBCWhen it receives a message, this outbound connector executes outside the transactional operation; the transaction continues and does not fail.
      Timeout-JMS   VM JDBCInsert an integer to represent the number of milliseconds (ms) that Mule allows to pass before it ends the transaction.
    3. If applying an XA transaction type to your connector, you have the option to check the Interact With External box. When checked, Mule acknowledges transactions that began externally. For example, if you set the transaction Action to BEGIN_OR_JOIN, and check Interact With External, Mule joins any transaction that is already in progress when it receives a message, regardless of whether the transaction began outside of Mule.
    4. If you applied an XA transaction to multiple connectors in your flow, access the global connectors each references, and configure the connectors to use XA-enabled resources.

    Use Transactions Configuration Reference for quick access to attribute configurations.

    1. Add a transactional child element to the inbound connector you wish to make transactional. 

      Child ElementAvailable on ConnectorUse
      jms:transactionJMSApply a transaction to a flow that involves a single resource (simple).
      jdbc-ee:transactionJDBCApply a transaction to a flow that involves a single resource (simple).
      vm:transactionVMApply a transaction to a flow which involves a single resource (simple).
      xa-transactionJMS VM JDBCApply a transaction to a flow that involves multiple resources.
      jms:client-ack-transactionJMSApply a transaction to a flow that involves multiple resources.

      ee:multi-transaction

      JMSApply a transaction to a flow that involves multiple resources.
    2. Configure transactional attributes:

      AttributeValueAvailable on ConnectorUse
      action




      NONEJMS VM JDBCWhen it receives a message, Mule resolves the transaction, then executes the operation as non-transactional.
      ALWAYS_BEGINJMS VM JDBCWhen it receives a message, Mule always starts a new transaction. If a transaction already exists, Mule resolves the transaction.
      BEGIN_OR_JOINJMS VM JDBCWhen it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.
      ALWAYS_JOINJMS   VM JDBCWhen it receives a message, Mule always expects a transaction to be in progress, and always joins the transaction. If no transaction is in progress, Mule throws an exception.
      JOIN_IF_POSSIBLEJMS   VM JDBCWhen it receives a message, Mule joins the current transaction if one is available. Otherwise, Mule does not begin a transaction.
      NOT_SUPPORTEDJMS VM JDBCWhen it receives a message, this outbound connector executes outside the transactional operation; the transaction continues and does not fail.
      timeout-JMS   VM JDBCInsert an integer to represent the number of milliseconds (ms) that Mule allows to pass before it ends the transaction.

      interactWithExternal

      true JMS VM JDBCWhen set to true, Mule acknowledges transactions that began externally. For example, if you set the transaction action to BEGIN_OR_JOIN, and set interactWithExternal to true, Mule joins any transaction that is already in progress when it receives a message, regardless of whether the transaction began outside of Mule.
    3. If you applied an XA transaction to multiple connectors in your flow, access the global connectors each references, and configure the connectors to use XA-enabled resources.

     View Namespace

    Use Transactions Configuration Reference for quick access to attribute configurations.

     

    Applying a Transaction as Wrapper

      Enterprise

      1. From the Scopes palette group, drag a Transactional scope onto the canvas. Drag building blocks into the Transactional scope to build your transaction.




        Alternatively, select multiple building blocks in a flow (shift+left click), then right-click to select Wrap in... > Transactional.
      2. Configure the details of the transaction according to the table below.

        FieldValueUse
        Display Name-Provide a meaningful name for the transaction scope in your flow.
        Type

        Simple TransactionDefault
        Apply a transaction to a flow that involves a single resource. See Single Resource Transaction for details.
        XA TransactionApply a transaction to a flow that involves multiple resources: JMS, VM or JDBC. See XA Transaction for details.
        Multi TransactionApply a transaction to a flow that involves multiple resources: JMS or VM. See Multiple Resource Transaction for details.
        ActionALWAYS_BEGINDefault
        When it receives a message, Mule always starts a new transaction.
        BEGIN_OR_JOINWhen it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.
      3. Drag building blocks inside the Transactional scope to build your transaction.



      Enterprise
      1. To your Mule flow, add one of the following types of transactional elements:

        Single Resource transaction
        <ee:transactional>
        </ee:transactional> 
        Multiple Resource transaction
        <ee:multi-transactional>
        </ee:multi-transactional>
        XA transaction
        <ee:xa-transactional>
        </ee:xa-transactional>
      2. Configure two attributes of the transactional element.

        AttributeValueDescription
        doc:name-Provide a meaningful name for the transaction scope in your flow. Not required in Standalone.
        actionALWAYS_BEGINWhen it receives a message, Mule always starts a new transaction.
        BEGIN_OR_JOINWhen it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.
      3. Add child elements inside your new transactional wrapper to build a transaction.

       View the Namespace



       

      Configuration Tips and Tricks

      • Operations that occur inside a transaction execute synchronously. You cannot build an asynchronous flow inside a transaction.
      • Mule creates a transaction for the first outbound connector that can be part of a transaction (JMS, JDBC, VM). All the outbound connectors in the flow that appear after the first outbound connector, and which use the same type of resource, then participate in the transaction. Where such a following connector does not use the same type of resource (such as where a JDBC connector follows a JMS connector), the transaction initiated by the first outbound connector fails. To avoid execution failure in such a situation, configure the secondary outbound connector outside the transaction by setting the action attribute to NOT_SUPPORTED.
      • If you apply an XA transaction to multiple connectors in your flow, be sure to configure the connectors to use XA-enabled resources.
      • If you apply an XA transaction to a JMS inbound connector in your flow, you have the option of specifying the polling frequency of the queue. Access XA Transactions for configuration details.
      • Mule can manage non-transactional outbound connectors. By default, an outbound connector from a non-transactional transport ignores an active transaction rather than rejecting it. In other words, the default transactional action for such connectors is no longer NONE. The example code below illustrates this behavior. Mule processes messages it receives from the VM queue synchronously and transactionally. The file transport in the code example is not transactional thus, writing to the file is not part of the transaction. However, if a message throws an exception while Mule is creating the file, Mule rolls back the transaction and reprocesses the message. This example is, in effect, a multiple resource transaction.
       View the Namespace

       

      Transaction Exception Strategies 

      To handle exceptions Mule throws while processing transactions, you have three options:

      1. Configure no exception strategies for the flow or transaction, thus employing Mule's default exception strategy. 
      2. Configure an exception strategy for the flow in which a transaction exists. The flow's exception strategy handles all exceptions Mule throws while processing the transaction.
      3. Configure an exception strategy for the scope of an individual transaction. The transaction's exception strategy handles all exceptions Mule throws while processing the transaction. If you wish to manage a transactional exception differently from all other exceptions thrown, consider applying an exception strategy to your transaction.

      Refer to the Error Handling documentation to learn more about Mule's default exception strategy and how to apply exception strategies to flows. Follow the steps below to apply an exception strategy to an individual transaction. 

        1. Add a Transactional scope to your flow (refer to steps above), then add building blocks within the scope to build a transaction.
        2. From the Error Handling palette group, drag and drop an exception strategy into the exception strategy section at the bottom of the scope. 



        3. Configure the exception strategy as needed, keeping in mind Mule uses this exception strategy to handle any exceptions thrown while processing the transaction. Reference the Error Handling documentation for exception strategy configuration details.
        1. Within your transactional wrapper, add an exception-strategy child element at the bottom of the wrapper.

        2. Configure the exception strategy as needed, keeping in mind Mule uses this exception strategy to handle any exceptions thrown while processing the transaction. Reference the Error Handling documentation for exception strategy configuration details.

         

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