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Transactional behavior of long-running BPEL processes

A long-running BPEL process spans multiple transactions. Each transaction is triggered either by a Java Messaging Service (JMS) message or by a work-manager-based implementation.

The following aspects of transactional behavior are described here:

• Overview
• Influencing transaction boundaries
• Concurrent navigation of parallel branches in flow activities
• Concurrent navigation of branches of a parallel forEach activity
• Invoked services and transactions in long-running processes
• Recovery from transaction failures
• Recovery of a successful service invocation when a transaction rolls back
• Recovery of a service invocation that results in a runtime exception

Overview

The following diagram shows how each navigation step in a long-running process is performed in its own transaction. A navigation step can span multiple activities as shown by the invoke activity that calls a service. Also, multiple activities can be run in one transaction as long as a transaction failure does not occur. For more information about transaction failures, see Recovery from transaction failures.

To allow navigation across transaction boundaries, the states of the process instance and its activity instances are persisted in the database.

You can influence transaction boundaries by using the transactional behavior attribute. However, Business Process Choreographer can add or remove transaction boundaries at any time.

In general, a transaction boundary is needed in the following situations:

• When waiting for an external request, that is, upon reaching a receive activity or pick activity (also known as a receive choice activity) in the process navigation for which a corresponding request has not been received yet

• When scheduling a timer for a wait activity

• When invoking a service asynchronously using an invoke activity

• When invoking a human task activity

In addition, Business Process Choreographer introduces transaction boundaries in the following situations. However, your process design must not rely on these boundaries because they can be overridden during process navigation, or they might change in the future.

• When a fault is raised during process navigation
• Before and after an invoke activity is started that invokes a service synchronously, and this service does not participate in the transaction of the process

• When propagating lifecycle operations to child processes, for example, when a parent process is suspended, its child processes are suspended in subsequent transactions

• When the process instance is to be deleted automatically upon completion of the process

• When trying to recover from a failure that causes the rollback of a transaction spanning a series of activities
• Where specified using the transactional behavior attribute

Influencing transaction boundaries

When you model a business process, you can suggest transaction boundaries for certain types of activities, such as, invoke, snippet, and human task activities by changing the transactional behavior attribute of the activity. The transactional behavior attribute is ignored if an invoke activity calls a synchronous service that does not participate in the current transaction. In this case, there is always a transaction boundary before the invoke activity is started, and after the invoke activity completes.

The attribute can take one of the following values:

Commit before

The current transaction is committed, and a new transaction is started. The activity with this attribute value becomes the first activity of the new transaction.

Commit after

The activity participates in the current transaction. After the activity completes successfully, the transaction is committed, and a new one is started. A new transaction is started for each immediately following activity, and each subsequent activity becomes the first activity of one of these new transactions.

Participates

The activity participates in the current transaction. Additional transaction boundaries are not set, neither before nor after the activity.

In the following situations, this setting allows the transaction to continue with the navigation of the following activities depending on the values of their settings of the transactional behavior attributes.

• If the invoke activity invokes the service asynchronously, the arrival of the response message triggers a new transaction. The transaction is short because it commits immediately after the status of the invoke activity is updated.

• In a sequence of human task activities, two transactions are needed for each human task activity, one to activate the human task activity and another to complete the human task activity. If you change the setting to Participates, you can reduce the number of transactions to one for each human task activity. This is because the completion of the previous human task activity, and the activation of the following activity are performed in the same transaction.

• To enable server-controlled page flows that use the completeAndClaimSuccessor API.

Requires own

The activity runs in its own transaction. This means that the current transaction is committed before the activity starts, and a new transaction starts after this activity completes.

You can also determine whether the transaction that initiates the process is committed after the receive activity, or the receive action of the receive-choice (pick) activity completes by changing the transactional behavior attribute of the corresponding activity. For initiating receive and receive-choice activities, the attribute can take one of the following values:

Commit after

After the activity completes successfully, the transaction that initiates the process is committed, and a new one is started. This setting is useful if you invoke the process instance using a synchronous API call.

Participates

The transaction that initiates the process continues after the activity completes. This setting is required if you want to invoke the process instance using the initiateAndClaimFirst API. With this API, you can create a process instance and immediately claim the first human task.

If your process invokes another BPEL process, ensure that the corresponding invoke activity is not part of the transaction that initiates the process. You can achieve by setting the transaction behavior attribute in one of the following ways:

• Set the attribute of the initiating receive or receive choice activity to Commit after
• Set the attribute of the invoke activity to Commit before or Requires own

Concurrent navigation of parallel branches in flow activities

To achieve concurrency in the navigation of parallel branches in a flow activity, a new transaction boundary is needed at the beginning of each branch so that each parallel activity is processed in a separate transaction. This means that the transactional behavior attribute of the first activity of each parallel branch must be set to Commit before or Requires own to achieve parallelism from the beginning of the flow.

For an Oracle database, navigation transactions for parallel branches in a process instance are serialized, that is they cannot be run in parallel. This is because the locks on database entities are not as granular as, for example, those for DB2 databases. However, services triggered asynchronously by such parallel branches still run in parallel; it is only the process navigation that is serialized for these database systems.

Concurrent navigation of branches of a parallel forEach activity

The processing of each branch of a parallel forEach activity is started in its own, separate transaction. Thus parallel execution of these branches is enabled.

For an Oracle database, navigation transactions for parallel branches in a process instance are serialized, that is they cannot be run in parallel. This is because the locks on database entities are not as granular as, for example, those for DB2 databases. However, asynchronous services on the branches of a parallel forEach activity are executed concurrently, thus parallelism forEach activities can be achieved.

Invoked services and transactions in long-running processes

A service that is called within a long-running process using an invoke activity can either participate in the current transaction of the long-running process, or it can run in its own transaction.

The following settings determine whether the service participates in the transaction of the long-running process or runs in its own transaction.

• The interaction style used to call the service.

  The interaction style can be synchronous or asynchronous. The style is determined by the preferred interaction style of the target SCA component or SCA import, as shown in the following table:

  Preferred interaction style of target component or import	One-way operation	Request-response operation
  Any	Asynchronous invocation	Asynchronous invocation
  Synchronous	Synchronous invocation	Synchronous invocation
  Asynchronous	Asynchronous invocation	Asynchronous invocation

• The Service Component Architecture transaction qualifiers that are specified for the process and the service that is called:

  • The suspendTransaction qualifier on the reference of the process component specifies whether the transaction context of the process is propagated to the services to be invoked.

  • The joinTransaction qualifier on the service interface specifies whether a service participates in the transaction of its caller if a transaction is propagated.

    Depending on the settings of the interaction style and the SCA qualifiers, the following rules apply to the invoked service:

    Synchronous invocation

    joinTransaction	suspendTransaction = true	suspendTransaction = false
    joinTransaction = true	The service does not participate in the transaction of the long-running process	The service participates in the transaction of the long-running process
    joinTransaction = false	The service does not participate in the transaction of the long-running process	The service does not participate in the transaction of the long-running process

    If a service participates in the current transaction of the long-running process, the changes that are made by the service to the transactional resources are persisted only if the current transaction commits.

    Asynchronous invocation

    The service always runs in its own transactions.

Recovery from transaction failures

A transaction in a long-running process can roll back for various reasons, such as:

• A server outage, for example, because of a power failure. The transaction is rolled back when the server is restarted.

• A failure in the Business Process Choreographer infrastructure, for example, a deadlock that causes a successful service invocation to roll back. Business Process Choreographer uses its internal queues to handle the failure. See Recovery of a successful service invocation when a transaction rolls back

• A rollback enforced by a service that was called from the process, for example, because a runtime exception thrown by an invoked service. See Recovery of a service invocation that results in a runtime exception

Recovery of a successful service invocation when a transaction rolls back

The recovery behavior depends on whether the called service participates in the current transaction.

An invoke activity calls a service that participates in the current transaction. The execution of the service is complete. If an error occurs after completion of the service and the transaction is rolled back to the state that the process was in before the transaction started, the effect of the called service is also rolled back. When the transaction is retried, the service is called again.

In contrast, if the called service does not participate in the current transaction and the called service returns a response, the response is stored in a separate transaction. If an error occurs after the response is stored, the current transaction is rolled back and the transaction is retried. During the retry the service is not called again, however, the stored response is restored and the navigation continues.

Recovery of a service invocation that results in a runtime exception

If a transaction fails because of a runtime exception, the message that triggered the transaction stays on the Business Process Choreographer internal queue for JMS navigation or in the work manager, and the message retry count is increased by one. The retry behavior depends on whether the transaction contains a single activity or spans multiple activities.

Transactions with a single activity

The activity is retried in a new transaction.

Transactions spanning multiple activities

When the transaction is retried, the transaction boundaries are scaled down so that the transaction is committed after each of the activities completes. In this way, the failure can be narrowed down to the activity that is causing the exception.

Example of scaling down transaction boundaries

A transaction step spans multiple activities {A1 through A n}.

If a runtime exception is returned by the activity A n, the transaction boundaries are scaled down to {A1} and {A2 through A n}.

If the activity A n returns the runtime exception again, the transaction boundaries are now scaled down to {A2} and {A3 through A n}. This adjustment of the transaction boundaries is repeated until the activity A n runs in its own transaction {A n}.

If the activity A n still returns the runtime exception, the exception is then stored in a local transaction. When the {A n} transaction in retried, the exception information is available without invoking the implementation of activity A n again.

The subsequent processing of the activity A n depends on the value of the Continue processing upon unhandled faults setting for the activity.

If you want a set of activities in a long-running process to always be invoked in a single transaction, factor out the business logic for these activities into a microflow, and invoke it as a subprocess. The logic of a microflow is always run in a single transaction.

Transactional behavior of BPEL processes

Related concepts:
Fault handling in BPEL processes
Recovery from infrastructure failures
Continue-on-error behavior of BPEL processes and activities

Related reference:
Server tab: BPEL process editor