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XA Resource Manager Swiftlet

The XA Resource Manager Swiftlet is the central XA resource to a router. Together with the JMS XA/ASF Swiftlet and the Routing Swiftlet, it is responsible for the administration of so-called in-doubt transactions. These are unfinished prepared XA transactions.

On startup, the XA Resource Manager Swiftlet checks if prepared XA transactions are stored within the Store Swiftlet. In this case, it reconstructs these transactions incl. all locks. A warning message is displayed during the startup with the hint to commit or abort these transactions manually.

Settings

The Swiftlet has 2 attributes to configure, a scanning interval and a transaction timeout.

Scan Interval

The Prepared XA Transactions node of the Swiftlet contains transactions in a prepared state. The update of this node consumes time and resources and is therefore made asynchronously. The scan interval value determines in which intervals the Swiftlet checks for pending XA transactions that are in a prepared state and enlists these below the Prepared XA Transactions node. The default value is 120000 ms (2 minutes) which is quite enough to enlist in-doubt XA transactions here for manual commit/rollback.

Default Transaction Timeout

A transaction timeout is a time after which a running and not yet prepared XA transaction is aborted (rolled back). The sense is to avoid long-running transactions and lock exhaustions. The value of this attribute is the default value. A transaction manager of an application server is able to get and set this value via the resp. methods of SwiftMQ's XAResource. The default value is 0 which means no timeout.

Heuristic Completion

Heuristic Branch Completion

According to the XA specification, a resource manager that has prepared to commit a transaction branch may decide to commit or roll back its work independently of the transaction manager. It could then unlock shared resources. This may leave them in an inconsistent state across the distributed transaction. This chapter explains how to perform heuristic commits and rollbacks of SwiftMQ XA transaction branches.

Heuristic Commit/Rollback via SwiftMQ Explorer App

The list of in-doubt transactions is located within the "Usage / Prepared XA Transactions" folder of the XA Resource Manager Swiftlet:

You have to select the respective transaction, and may now choose between commit/rollback.

Heuristic Commit/Rollback via CLI

Example:

XML
    Welcome to SwiftMQ!

    Username:
    Password:
    Trying to connect ... connected
    Type 'help' to get a list of available commands.
    > Router 'router1' is available for administration.

    > sr r
    router1> cc sys$xa
    router1/sys$xa> cc usage/prepared-tx
    router1/sys$xa/usage/prepared-tx> lc

    Entity List: Prepared XA Transactions
    Description: Prepared XA Transactions

    Entities in this List:
    ----------------------
    1
    2
    3
    4

    router1/sys$xa/usage/prepared-tx> rollback 3
    router1/sys$xa/usage/prepared-tx> commit 4
    router1/sys$xa/usage/prepared-tx> lc

    Entity List: Prepared XA Transactions
    Description: Prepared XA Transactions

    Entities in this List:
    ----------------------
    1
    2

    router1/sys$xa/usage/prepared-tx>

Heuristically completed XA Transactions

According to the XA specification, an XA resource has to store information about heuristically completed XA transactions until the driving transaction manager commands to forget it. Therefore, when an XA transaction has been heuristically completed with SwiftMQ Explorer App or CLI, it is still stored under the folder Usage / Heuristically completed XA Transactions until the recovery is started by a transaction manager:

If automatic recovery is not done by a transaction manager for any reason, the entries can be manually deleted.

Configuration

The configuration of the XA Resource Manager Swiftlet is defined within the element

XML
      <swiftlet name="sys$xa" .../>

of the router's configuration file.

Attributes of Element "swiftlet"

Definition

Attribute

Type

Mandatory

Description

scan-interval

java.lang.Long

No

Interval to scan prepared XA transaction to put into the Usage List

default-transaction-timeout

java.lang.Long

No

Max. time a XA transaction can run, thereafter it will be rolled back

Values

Attribute

Values

scan-interval

Min: 500
Default: 120000

default-transaction-timeout

Min: 0
Default: 0

Element "usage", Parent Element: "swiftlet"

Usage.

Element List "prepared-tx", Parent Element: "usage"

Prepared XA Transactions. This element list contains zero or more "prepared-xa-transaction" elements with this template definition:

Definition

Attribute

Type

Mandatory

Description

name

java.lang.String

Yes

Name of this Prepared XA Transaction

xid

java.lang.String

No

Xid (Internal Representation)

Values

Attribute

Values

xid

Element List "heuristic-tx", Parent Element: "usage"

Heuristically completed XA Transactions. This element list contains zero or more "heuristic-xa-transaction" elements with this template definition:

Definition

Attribute

Type

Mandatory

Description

name

java.lang.String

Yes

Name of this Heuristically completed XA Transaction

xid

java.lang.String

No

Xid (Internal Representation)

operation

java.lang.String

No

Operation

Values

Attribute

Values

xid

operation

Choice: COMMIT ROLLBACK

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