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Distributed Transaction
&
Long-running transactions
Krasimir Parushev
Consultant, ITCE ltd.
Rossen Zhivkov
Freelance SharePoint Consultant
January 19th, 2008
Sofia, Bulgaria
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?
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, WSBusiness Activity
What is BPEL4WS
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
Local Transactions
Client 1
VB
Object
ADO
Conn
Lock
Manager
Transaction
Manager
Activity
Client 2
ADO
Conn
VB
Object
Activity
Client N
Data
ADO
Conn
VB
Object
Activity
Application
DBMS
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
A Distributed Transaction
RM2 -SQL Server
RM1 - MSMQ
Your Tx COM+ Application
RM Proxy
Queue
RM Proxy
The Coordinating DTC
Computer 1
Data
Participating
ComputerDTC
2
RM Proxy
RM3 - ORACLE
Data
Participating
ComputerDTC
3
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
Two-Phase Commit
Transaction Manager
Dispenses new transactions
to clients
Tracks the resource
managers participating in the
transaction
Coordinates the
transaction
outcome
Transaction
Manager
Resource Manager
A subsystem that
allows updates to
transaction
protected data
SQL
Server
File
System
Resource
Managers
SQL
Server
Resource
Manager
Two-Phase Commit
Transaction
Manager
Resource
Manager
Prepare
Prepared
Force write “Commit”
record to TM log
Lazy write “Committed”
record to TM log
Prepare and Force write
“Prepared” record to RM log
Commit
Committed
Lazy write “Committed” record
to RM log and Release locks
Commit
Abort on
Failure
Committed
Will
Will
Commit Abort
Commit
Write “Committed”
record to TM log
Resource
Manager
Prepared
Indoubt
on Failure
Write “Commit”
record to TM log
Prepare
Commit
Transaction
Manager
Abort on Failure
Two Phase Commit – Failure
Prepare & Write
“Prepared” record to
RM log
Write “Committed”
record to RM log &
Release locks
LIVE DEMO
MS-DTC
Distributed 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, …
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
ITransactionJoin::JoinTransaction
ADO
Only implicit via MTS/COM+
System.Data.SqlClient
v1.1 SqlConnection.EnlistDistributedTransaction
System.Transactions
Later…
DB-Library – dbenlisttrans
COM+, System.EnterpriseServices, WCF
SQL Server And Dist. Tx…
Server initiated
BEGIN DISTRIBUTED TRANSACTION
Linked Server call
Extended Stored Procedures
X-Transactions
Application
Partitioned Tables
MS DTC
MS DTC
SQL
Server
NT
SQL
Server
NT
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
Transaction Flow
Transaction A
Code block with
no ambient
transaction
----- -- - - -- -- --- –- – - - ---- -- –-- –- - –-- ------ -- - - –- –- –
scope 1
{Required}
scope 2
{Required}
Transaction B
scope 3
scope 4
{RequiresNew}
{Suppress}
Transactions from .NET application
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
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
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
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
Incorporate web services in distributed
transactions using WCF
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
LIVE DEMO : Long-running transactions
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 WSAtomicTransaction services
Compensations
SOAP “compensate” message
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
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
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
Implement long-running transactions in
Windows Workflow Foundation
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 & WSAtomicTransaction
Long-running transactions
Workflow Foundation
BPEL4WS & WS-BusinessActivity
Next steps
Thank You
for you time
Rossen Zhivkov
[email protected]
Krasimir Parushev
[email protected]