Distributed Transaction

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Distributed Transaction Long-running
transactions
Krasimir ParushevConsultant, ITCE ltd.

• Rossen ZhivkovFreelance SharePoint Consultant

January 19th, 2008Sofia, Bulgaria
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What if

• What if you have to update a SQL Server database
  and Oracle database in one transaction?
• What if you have to call two web services in one
  transaction?
• What if you have to implement transaction that
  lasts for days?

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What is

• What is distributed transaction
• What is 2-phase commit protocol
• What is transaction coordinator
• What is resource manager
• What is long-running transaction
• WS-Coordination, WS-AtomicTransaction,
  WS-Business Activity
• What is BPEL4WS

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Roles in Transaction System

• Application
• Begins the transaction
• Makes changes to resources
• Can Commit or Abort the transaction
• Transaction Manager
• Transaction demarcation, participants, and state
• Prepare result is made durable
• Can Abort the transaction
• Resource Managers
• Controls changes to resources under the scope of
  a transaction
• Uses a (durable) log for recovery
• Can Abort the transaction
• Need to participate in 2PC (Atomicity)
• Provide Isolation of its resources
• Provide Durability of its resources

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Local Transactions
Application
DBMS
Activity
Transaction Manager
Lock Manager
Client 1
Activity
Client 2
Data
Activity
Client N
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Local Transactions

• All updates within a single DBMS
• Or other resource manager (RM)
• DBMS provides transaction demarcation
• Begin (start), end (commit), abort (rollback)
• DBMS provides transaction manager
• DBMS provide lock manager

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A Distributed Transaction
Data
Your Tx COM Application
RM Proxy
Queue
RM Proxy
RM Proxy
Data
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Distributed Transactions

• Transactions may span multiple RMs
• Databases, Queues, etc.
• Distributed Transaction Manager
• Provides common transaction demarcation
• Coordinates commit/abort across RMs
• 2 Phase Commit (2PC) Protocol
• RMs are prepared to either commit or abort
• RMs are notified of final outcome
• RM recovery
• Resource Managers
• Need to participate in 2PC (Atomicity)
• Provide Isolation of its resources
• Provide Durability of its resources

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Two-Phase Commit

• Transaction Manager
• Dispenses new transactions to clients
• Tracks the resource managers participating in the
  transaction
• Coordinates the transaction outcome
• Resource Manager
• A subsystem that allows updates to transaction
  protected data

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Two-Phase Commit
Resource Manager
Transaction Manager
Prepare
Prepare and Force write Prepared record to RM
log
Prepared
Force write Commit record to TM log
Commit
Lazy write Committed record to RM log and
Release locks
Committed
Lazy write Committed record to TM log
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Two Phase Commit Failure
Resource Manager
Transaction Manager
Abort on Failure
Prepare
Abort on Failure
Prepare Write Prepared record to RM log
Prepared
Will Abort
Write Commit record to TM log
Indoubt on Failure
Commit
Will Commit
Write Committed record to RM log Release locks
Commit
Committed
Commit
Write Committed record to TM log
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Two Phase Commit

• Transaction manager coordinates updates made by
  resource managers
• Phase 1
• Prepare to commit
• Phase 2
• Commit
• Transaction manager always knows the state of the
  transaction

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Phase 1

• Transaction manager asks all RMs to prepare to
  commit.
• RMs can save their intended changes and then say
  yes.
• Any RM can say no.
• No RM actually commits yet!
• If all RMs said yes, go to Phase 2.
• If any RMs said no, tell everyone to abandon
  their intended changes.

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Phase 2

• Transaction manager asks all resource managers to
  go ahead and commit their changes.
• Can now recover from failure
• RM knows what transactions were questionable at
  point of failure
• TM knows whether transactions succeeded or failed

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LIVE DEMO
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MS-DTCDistributed Transaction Coordinator

• Windows NT Service
• Two Phase Commit (2PC) and Recovery
• Infrastructure
• COM Interfaces (a.k.a., DTC proxy)
• Used for App ? TM, TM ?RM communication
• Local TM, remote TM, TM failover
• Supported Resource Managers (RM)
• SQL Server, MSMQ, BizTalk, COM CRM,
• Oracle, DB2,

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SQL Server And Dist Tx

• Client initiated distributed transaction
• Existing DTC transaction is passed to SQL Server
  using data access API
• ODBC
• SQL_ATTR_ENLIST_IN_DTC connection attribute
• OLE-DB
• ITransactionJoinJoinTransaction
• ADO
• Only implicit via MTS/COM
• System.Data.SqlClient
• v1.1 SqlConnection.EnlistDistributedTransaction
• System.Transactions
• Later
• DB-Library dbenlisttrans
• COM, System.EnterpriseServices, WCF

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SQL Server And Dist. Tx

• Server initiated
• BEGIN DISTRIBUTED TRANSACTION
• Linked Server call
• Extended Stored Procedures
• X-Transactions
• Partitioned Tables

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Using distributed transactions in .NET
System.Transactions

• System.Transactions API for programming local
  distributed transactions
• Enlisting resources in distributed transactions
• Ambient Transactions
• Transaction Promotion
• Transaction Flow

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Transaction Flow
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Transactions from .NET application
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Custom Resource Managers

• Why to write own resource managers
• Incorporate custom resources in distributed
  transactions
• Implement logic for two-phase commit steps
  (Prepare, Commit, Rollback)
• Volatile resource managers
• Transactional variables
• Transactional collections
• Transactional files.
• Sample

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Transactional NTFS Registry

• Kernel Transaction Memory
• Kernel objects in transaction (distributed /
  local)
• Allows atomic operations for
• Many operations on single file
• Operations for multiple files
• Operations for many computers
• Registry modifications
• Sample

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Windows Communication Foundation

• What is WCF?
• Web services WSE WS-specifications MSMQ
  EnterpriseServices(COM) Remoting
• Reliable messaging
• Securable services
• Protocols support
• New abstraction level
• Data Abstraction
• Communication Abstraction

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WCF and Transactions

• WCF services other resource managers can be
  executed within the scope of distributed
  transaction
• Transactable Services
• In the Internet using WS-AtomicTransaction
• In the Intranet - DTC, OleTransaction protocol,
  System.Transaction
• MSDTC and WS-AtomicTransactions
• Transaction Flow

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Incorporate web services in distributed
transactions using WCF
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Long-running transactions

• The business scenario
• We cannot lock the service sessions (and the
  underlying database) for that long time
• Are ACID properties maintained?
• Is it OK to hold locks for days
• Compensation actions
• Logic to undo the effects from previously
  committed action

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LIVE DEMO Long-running transactions
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WS- specifications

• WS-Coordination
• Distribution of the transaction context
• WS-AtomicTransaction
• Pure ACID for short transactions with 2PC or
  similar
• Locking resources
• WS-Business Activity
• Long living transactions
• To coordinate large work implemented by several
  small WS-AtomicTransaction services
• Compensations
• SOAP compensate message

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Business Process Execution Language For Web
Services - BPEL4WS

• What is BPEL4WS
• Orchestrating web services to implement business
  process
• Complex transactions modeled as WORKFLOW
• Provides sequences, branches, iterations, etc
• Bound to local scope
• Use WS-BusinessActivity to incorporate
  distributed scopes

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Comparison Distributed vs. Long-running

• Transaction trees
• In distributed transactions
• Parent NEVER commits before the child commits
  (2PC)
• Parent / Child hold locks till end of transaction
• In long-running transactions
• Parent can commit independently of the child
  transaction
• If Child then rollbacks, parent executes
  compensation logic
• Parent / Child release locks immediately after
  commit

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Workflow Foundation

• Business Processes orchestration
• Support for Distributed transactions via
  TransactionScope
• Support for Long-running transactions via
  Compensations
• Persistence and Tracking
• Integration with WCF Web Services
• Published as WCF/web service
• Utilizes WCF/Web service

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Implement long-running transactions in Windows
Workflow Foundation
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Summary

• Distributed Transactions
• 2-Phase Commit Protocol
• SQL Server 2005 Distributed transactions
• .NET Distributed Transactions
• Custom Resource Managers
• Distributed Transactions in Web Services
• Windows Communications Foundation
  WS-AtomicTransaction
• Long-running transactions
• Workflow Foundation
• BPEL4WS WS-BusinessActivity
• Next steps

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Thank You for you time
Rossen Zhivkovrzhivkov_at_gmail.com
Krasimir Parushevkrasimir_at_itce.com