WS Transaction Specs

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WS Transaction Specs

• Gokce Banu Laleci
• METU-SRDC

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Transactions

• Distributed system
• Reliability problems
• Subject to independent failure of any of its
  components
• Decentralization allows
• Parts of the system fail
• Other parts remain functioning
• Abnormal behavior

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ACID Properties

• Atomicity The transaction completes successfully
  (commits) or if it fails (aborts) all of its
  effects are undone (rolled back)
• Consistency Transactions produce consistent
  results and preserve application specific
  invariants
• Isolation Intermediate states produced while a
  transaction is executing are not visible to other
  transactions
• appear to execute serially
• achieved by locking resources
• Durability The effects of a committed
  transaction are never lost (except by a
  catastrophic failure)s

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Atomic Transactions

• can be terminated in two ways
• Committed
• all changes made within it are made durable
• Aborted (rolled back)
• all changes made during the lifetime of the
  transaction are undone

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Why Atomic transactions may be too strong

• Suitable for short lived applications
• Long-lived transactions may reduce the
  concurrency
• By holding onto resources for a long time
• If it aborts
• Much valuable work already performed will be
  undone
• Pure ACID transactions are not suitable for Web
  Services
• WS Transactions
• Atomic transactions
• Business Activities

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A Suit of Specifications

• As a response to these needs in July 2002, BEA,
  IBM, and Microsoft released a trio of
  specifications designed to support business
  transactions over Web services
• BPEL4WS,
• WS-Transaction, and
• WS-Coordination

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Two Distinct Models

• WS-Transaction specification proposes two
  distinct models
• Atomic transaction (AT) Model is used to
  coordinate activities having a short duration and
  executed within limited trust domains
• Business Activity (BA) Model is used to
  coordinate activities that are long in duration
  and desire to apply business logic to handle
  business exceptions

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WS-C WS-TX

• WS-C
• Provides a generic framework for coordination
  protocols to be plugged in

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Participants Transaction aware Web services
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Participants Transaction aware Web services
JAXTX
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Atomic Transactions

• Similar to traditional ACID transactions
• Services enroll transaction-aware resources
• Databases
• Message queues

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The Players

• Completion Initiator
• Application
• Signals coordinator to complete a transaction
• Can request commit or rollback
• Coordinator
• Responsible for coordinating a single outcome
• Drives 2PC with participants
• Phase 1 Ensure all participants are prepared
• Phase 2 Notify participants of outcome
• Participants
• can vote to abort
• Can vote prepared to commit
• Must honor coordinators commit decision

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Protocols

• Completion
• Client application

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Coordinators Completion Service
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Participants Completion Service
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(Another advantage)

• traditional transaction systems talk to one
• opportunity to leverage an unparalleled
  interoperability technology to splice together
  existing transaction processing systems that
  already form the backbone of enterprise level
  applications

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Protocols

• 2PC

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Other protocols

• CompletionWithAck
• Same as Completion, but the coordinator must
  remember the outcome until receipt of an
  acknowledgment notification
• PhaseZero
• A participant that wants the coordinator to
  notify it just before the 2PC protocol begins
  registers for this A typical example is an
  application that caches data and needs a
  notification to write outstanding updates to a
  database
• OutcomeNotification
• A transaction participant that wants to be
  notified of the commit-abort decision registers
  for this

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A walkthrough
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Step1

• An application creates a transactional activity
  using the WS-Coordination framework's Activation
  Service

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Step1

• Coordination Service returns
• Coordination Context
• includes the address of the Registration

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Step 2

• The application defines itself as the artifact
  responsible driving the Completion protocol to
  complete the activity
• The role of coordinator is defined within the
  Coordination Service
• the CoordinatorRef is returned on the call
• application uses later to invoke the Completion
  protocol

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Step2
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Step3

• The application performs some operation on a Web
  service

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Step4- Service Registers 2PC
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Step 5- Registration Service Responds
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Step6 WS returns result
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Step 7 Application commits
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Step8 Coordinator sends Prepare
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Step 9 WS-Participant sends prepared
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Step 10 Coordinator sends commit
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Step 11 WS-Participant sends committed
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Business Activity
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• short running atomic transactions can be part
• of a long running business transaction. The
  actions of the embedded atomic transactions are
  committed and made visible before the
• long running business transaction completes, and
  in the event of the long running business
  transaction failing, the effects of such
• atomic transactions need to be compensated for,
  that is, open nested transactions.