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Transaction Management

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

The following endpoints support transactional demarcation:

  • JMS

  • JDBC

  • VM

However, there may be situations in which a Mule flow begins with a non-transactional inbound endpoint – 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 some of the characteristics of each type.

Type Characteristics Number of Resources Available Resources Performance

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, on the other hand, are more reliable and 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.

Configuring Transactions

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

  • Apply a transaction to an inbound endpoint when you want Mule to handle the complete flow as a transaction.

  • Apply a transaction to an outbound endpoint 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 a you want to apply a transaction to elements within a flow which do not begin with a inbound endpoint 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)

Studio Visual Editor

  1. In the endpoint’s properties panel, click the General tab to access the Transaction pane (see image below of the JMS endpoint).

    transactions_panel

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

    Attribute Value Available on Endpoint Use

    Type

    JMS Transaction

    JMS

    Apply a transaction to a flow which involves a single resource (simple).

    JDBC Transaction

    JDBC

    Apply a transaction to a flow which involves a single resource (simple).

    VM Transaction

    VM

    Apply a transaction to a flow which involves a single resource (simple).

    XA Transaction

    JMS VM JDBC

    Apply a transaction to a flow which involves multiple resources.

    Client Ack Transaction

    JMS

    Apply a transaction to a flow which involves multiple resources.

    Multi-resource Transaction

    JMS VM JDBC

    Apply a transaction to a flow which involves multiple resources.

    Action

    NONE

    JMS VM JDBC

    When it receives a message, Mule resolves the transaction, then executes the operation as non-transactional.

    ALWAYS_BEGIN

    JMS VM JDBC

    When it receives a message, Mule always starts a new transaction. If a transaction already exists, Mule resolves the transaction.

    BEGIN_OR_JOIN

    JMS VM JDBC

    When it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.

    ALWAYS_JOIN

    JMS VM JDBC

    When 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_POSSIBLE

    JMS VM JDBC

    Default When it receives a message, Mule joins the current transaction if one is available. Otherwise, Mule does not begin a transaction.

    NOT_SUPPORTED

    JMS VM JDBC

    When it receives a message, this outbound endpoint executes outside the transactional operation; the transaction continues and does not fail.

    Timeout

    -

    JMS VM JDBC

    Insert 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 endpoint, you have the option to check the Interact With External box. When checked, Mule acknowledges transactions which 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 endpoints 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.

Studio or Standalone XML

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

    Child Element Available on Endpoint Use

    jms:transaction

    JMS

    Apply a transaction to a flow which involves a single resource (simple).

    jdbc-ee:transaction

    JDBC

    Apply a transaction to a flow which involves a single resource (simple).

    vm:transaction

    VM

    Apply a transaction to a flow which involves a single resource (simple).

    xa-transaction

    JMS VM JDBC

    Apply a transaction to a flow which involves multiple resources.

    jms:client-ack-transaction

    JMS

    Apply a transaction to a flow which involves multiple resources.

    ee:multi-transaction

    JMS

    Apply a transaction to a flow which involves multiple resources.

  2. Configure transactional attributes according to the table below.

    Attribute Value Available on Endpoint Use

    action

    NONE

    JMS VM JDBC

    When it receives a message, Mule resolves the transaction, then executes the operation as non-transactional.

    ALWAYS_BEGIN

    JMS VM JDBC

    When it receives a message, Mule always starts a new transaction. If a transaction already exists, Mule resolves the transaction.

    BEGIN_OR_JOIN

    JMS VM JDBC

    When it receives a message, Mule joins a transaction if one is already in progress. Otherwise, Mule simply begins a new transaction.

    ALWAYS_JOIN

    JMS VM JDBC

    When 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_POSSIBLE

    JMS VM JDBC

    When it receives a message, Mule joins the current transaction if one is available. Otherwise, Mule does not begin a transaction.

    NOT_SUPPORTED

    JMS VM JDBC

    When it receives a message, this outbound endpoint executes outside the transactional operation; the transaction continues and does not fail.

    timeout

    -

    JMS VM JDBC

    Insert an integer to represent the number of milliseconds (ms) that Mule allows to pass before it ends the transaction.

    interactWithExternal

    true

    JMS VM JDBC

    When set to true, Mule acknowledges transactions which 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 endpoints in your flow, access the global connectors each references, and configure the connectors to use XA-enabled resources.

    View Namespace

<mule xmlns:jms="http://www.mulesoft.org/schema/mule/jms"
...
xmlns:xsi="
http://www.mulesoft.org/schema/mule/jms http://www.mulesoft.org/schema/mule/jms/current/mule-jms.xsd">
<jms:inbound-endpoint doc:name="JMS">
            <xa-transaction action="ALWAYS_BEGIN" timeout="35000"/>
</jms:inbound-endpoint>

Use Transactions Configuration Reference for quick access to attribute configurations.

Applying a Transaction as Wrapper

Studio Visual Editor

Enterprise

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

    scope2

    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.

    Field Value Use

    Display Name

    -

    Provide a meaningful name for the transaction scope in your flow.

    Type

    Simple Transaction

    Default

    Apply a transaction to a flow that involves a single resource. See Single Resource Transaction for details.

    XA Transaction

    Apply a transaction to a flow which involves multiple resources: JMS, VM or JDBC. See XA Transaction for details.

    Multi Transaction

    Apply a transaction to a flow which involves multiple resources: JMS or VM. See Multiple Resource Transaction for details.

    Action

    ALWAYS_BEGIN

    Default

    When it receives a message, Mule always starts a new transaction.

    BEGIN_OR_JOIN

    When 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.

    add_blocks

Studio or Standalone XML

Enterprise

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

    Single Resource transaction

    <ee:transactional> </ee:transactionl>

    Multiple Resource transaction

    <ee:xa-transactional> </ee:xa-transactional>

    XA transaction

    <ee:multi-transactional> </ee:multi-transactional>

  2. Configure two attributes of the transactional element.

    Attribute Value Description

    doc:name

    -

    Provide a meaningful name for the transaction scope in your flow. Not required in Standalone.

    action

    ALWAYS_BEGIN

    When it receives a message, Mule always starts a new transaction.

    BEGIN_OR_JOIN

    When 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.

    Namespace:

    <mule xmlns:vm="http://www.mulesoft.org/schema/mule/vm"
...
xmlns:xsi="
http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/current/mule-vm.xsd">

    Body:

    <flow>
...
   <transactional action="BEGIN_OR_JOIN">
      <vm:outbound-endpoint path="out1"/>
      <vm:outbound-endpoint path="out2"/>
      <custom-processor class="org.mule.example.FailingMessageProcessor"/>
      <catch-exception-strategy>
         <vm:outbound-endpoint path="dead.letter.queue"/>
      </catch-exception-strategy>
   </transactional>
...
</flow>

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 endpoint that can be part of a transaction (JMS, JDBC, VM). All the outbound endpoints in the flow which appear after the first outbound endpoint and which use the same type of resource then participate in the transaction. Where such a following endpoint does not use the same type of resource (i.e. where a JDBC endpoint follows a JMS endpoint), the transaction initiated by the first outbound endpoint fails. To avoid execution failure in such a situation, configure the secondary outbound endpoint outside the transaction by setting the action attribute to NOT_SUPPORTED.

  • If you apply an XA transaction to multiple endpoints in your flow, be sure to configure the connectors to use XA-enabled resources.

  • If you apply an XA transaction to a JMS inbound endpoint 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 endpoints. By default, an outbound endpoint from a non-transactional transport ignores an active transaction rather than rejecting it. In other words, the default transactional action for such endpoints 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 will roll back the transaction and reprocess the message. This example is, in effect, a multiple resource transaction.

Namespace:

<mule xmlns:vm="http://www.mulesoft.org/schema/mule/vm"
...
xmlns:xsi="
http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/current/mule-vm.xsd">

Body:

<flow name="transactionalVM">
    <vm:inbound-endpoint path="orders" exchange-pattern="one-way">
        <vm:transaction action="ALWAYS_BEGIN"/>
     </vm:inbound-endpoint>
     <file:outbound-endpoint ref="receivedOrders"/>
</flow>

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 by default.

  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.

Studio Visual Editor

  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.

    exception_strategy

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

Studio or Standalone XML

  1. Within your transactional wrapper, add an exception-strategy child element at the bottom of the wrapper.

    <ee:multi-transactional action="ALWAYS_BEGIN" doc:name="Transactional">
            <jdbc-ee:outbound-endpoint exchange-pattern="one-way" queryTimeout="-1" doc:name="Database"/>
            <rollback-exception-strategy doc:name="Rollback Exception Strategy"/>
        </ee:multi-transactional>

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

See Also