Honor that TransactionHonor that TransactionHow to Design and Code Your How to Design and Code Your TransactionsTransactions

Vineet GuptaVineet GuptaEvangelist – Database and IntegrationEvangelist – Database and IntegrationMicrosoft Corp.Microsoft Corp.

http://spaces.msn.com/members/vineetgupta/http://spaces.msn.com/members/vineetgupta/

Why Transactions?Why Transactions?Correctness (programming model)Correctness (programming model)ACID propertiesACID properties

AtomicityAtomicityAll changes happen or nothing happensAll changes happen or nothing happens

ConsistencyConsistencyData is transformed from one correct state to anotherData is transformed from one correct state to another

IsolationIsolationConcurrent updaters are prevented from interfering with Concurrent updaters are prevented from interfering with one anotherone another

DurabilityDurabilityCommitted changes remain permanent despite failuresCommitted changes remain permanent despite failures

Scenario: Bank Funds TransferScenario: Bank Funds TransferClassicalClassical

Savings

Checking

Withdraw from savings

Deposit into checking

Begin SQL Transaction

Commit SQL Transaction

Database

Single Machine

Client-ServerClient-Server

Savings

Checking

Withdraw from savings

Deposit into checking

Begin SQL Transaction

Commit SQL TransactionDatabase

Machine 1 Machine 2

Three-Tier ComponentsThree-Tier Components

Savings

Checking

Database

Withdraw

Deposit

Transfer

TM

Begin Tx

Commit Tx

Log

RM DistributionRM Distribution

Savings

Checking

Withdraw

Deposit

Transfer

TM

Begin Tx

Commit Tx

Log

Roles in Transaction SystemsRoles in Transaction Systems

Transaction ManagerTransaction Manager•Transaction demarcation, participants, and stateTransaction demarcation, participants, and state•Prepare result is made durablePrepare result is made durable•Can Abort the transactionCan Abort the transaction

Resource ManagerResource Manager•Controls changes to resourcesControls changes to resources•Uses a (durable) log for recoveryUses a (durable) log for recovery•Can Abort the transactionCan Abort the transaction

Client ApplicationClient Application•Begins the transaction,Begins the transaction,•Makes changes to resources, Makes changes to resources, •Can Commit or Abort the transactionCan Commit or Abort the transaction

Resource ManagerResource Manager

Resource ManagementResource ManagementACID Transaction Design RequirementsACID Transaction Design Requirements

Atomicity Consistency Atomicity Consistency IsolationIsolation DurabilityDurability

Isolation:Isolation: A transaction either A transaction either Sees data in the state it was in Sees data in the state it was in beforebefore another concurrent transaction modified it, another concurrent transaction modified it, Or it sees the data Or it sees the data afterafter the second the second transaction has completed, transaction has completed, But it But it does notdoes not see an see an intermediateintermediate state state

Isolation LevelsIsolation LevelsPerfect Isolation of Transactions Leads Perfect Isolation of Transactions Leads to Resource Contentionto Resource ContentionWe actually use We actually use Degrees of IsolationDegrees of Isolation

Common NameCommon Name

DegreeDegree

A.K.A.A.K.A.

Lost Updates?Lost Updates?

Dirty Reads?Dirty Reads?

Unrepeatable Reads?Unrepeatable Reads?

Phantoms?Phantoms?

00

ChaosChaos

YesYes

YesYes

YesYes

YesYes

11

Read Read UncommittedUncommitted

BrowseBrowse

YesYes

NoNo

YesYes

YesYes

22

Read Read CommittedCommitted

Cursor Cursor StabilityStability

NoNo

NoNo

YesYes

YesYes

33

SerializableSerializable

IsolatedIsolated

NoNo

NoNo

NoNo

NoNo

2.9992.999

RepeatableRepeatableReadRead

NoNo

NoNo

NoNo

YesYes

SQL-2000 lockingSQL-2000 locking

Row-1Row-1

Tran2 (Select)Tran2 (Select)Tran1 (Update)Tran1 (Update)

X-LockX-Lock S-LockS-Lock BlockedBlockedRow-1Row-1

Microsoft® SQL Server™ 2005 Microsoft® SQL Server™ 2005 Isolation Level ExtensionsIsolation Level Extensions

Read-Committed Snapshot IsolationRead-Committed Snapshot IsolationNew flavor of read committed (non-locking)New flavor of read committed (non-locking)Statement-level Snapshot IsolationStatement-level Snapshot IsolationSee most recent committed value of data as of the See most recent committed value of data as of the start of the start of the statementstatement

Snapshot IsolationSnapshot IsolationNew isolation levelNew isolation levelTransaction-level Snapshot IsolationTransaction-level Snapshot IsolationSee most recent committed value of data as of the See most recent committed value of data as of the start of the start of the transactiontransaction

SQL Server 2005 Isolation Levels SQL Server 2005 Isolation Levels

Isolation LevelsIsolation Levels Dirty Dirty ReadRead

Non-Non-Repeatable Repeatable

ReadReadPhantomsPhantoms Update Update

ConflictConflictConcurrency Concurrency

ControlControl

Read Read UncommittedUncommitted YesYes YesYes YesYes NoNo

Read Read CommittedCommitted

1 Locking1 Locking22 Snapshot Snapshot

NoNoNoNo

YesYesYesYes

YesYesYesYes

NoNoNoNo

PessimisticPessimisticOptimisticOptimistic

Repeatable Repeatable ReadRead NoNo NoNo YesYes NoNo PessimisticPessimistic

SnapshotSnapshot NoNo NoNo NoNo Yes Yes OptimisticOptimistic

SerializableSerializable NoNo NoNo NoNo NoNo PessimisticPessimistic

Possible AnomaliesPossible Anomalies

Read-Committed SnapshotRead-Committed Snapshot

New “flavor” of read committedNew “flavor” of read committedRequires a database-level settingRequires a database-level settingReaders see committed values as of Readers see committed values as of beginning of statementbeginning of statement

Writers do not block ReadersWriters do not block ReadersReaders do not block WritersReaders do not block WritersWriters Writers dodo block Writers block Writers

Can greatly reduce locking / deadlocking Can greatly reduce locking / deadlocking without changing applicationswithout changing applications

Snapshot IsolationSnapshot IsolationRepresents a new isolation levelRepresents a new isolation levelTransitionally consistent database as of Transitionally consistent database as of the beginning of the transactionthe beginning of the transaction

Requires session-level settingRequires session-level settingReaders do not lock data Readers do not lock data Reduces deadlocksReduces deadlocks

But at a cost of write-write conflictsBut at a cost of write-write conflictsSnapshot Isolation state is ON by default for Snapshot Isolation state is ON by default for mastermaster and and msdbmsdb

Isolation Levels: In SummaryIsolation Levels: In Summary

READ UNCOMMITTED (Level 0)READ UNCOMMITTED (Level 0)““Dirty Reads” – An option ONLY for readersDirty Reads” – An option ONLY for readersAny data (even that which is in-flight/locked) can Any data (even that which is in-flight/locked) can be viewedbe viewed

READ COMMITTED (Level 1 – Default)READ COMMITTED (Level 1 – Default)Only committed changes are visibleOnly committed changes are visibleData in an intermediate state cannot be accessedData in an intermediate state cannot be accessed

READ COMMITTED SNAPSHOT (RCSI)READ COMMITTED SNAPSHOT (RCSI)Statement-level read consistencyStatement-level read consistencyNew non-blocking, non-locking (ex. SCH_S), New non-blocking, non-locking (ex. SCH_S), version-based Level 1version-based Level 1

Isolation Levels: In Summary (cont’d)Isolation Levels: In Summary (cont’d)

REPEATABLE READS (Level 2)REPEATABLE READS (Level 2)All reads are consistent for the life of a transactionAll reads are consistent for the life of a transactionShared locks are NOT released after the data is Shared locks are NOT released after the data is processedprocessedDoes not protect entire set (i.e. phantoms may occur)Does not protect entire set (i.e. phantoms may occur)

SERIALIZEABLE (Level 3)SERIALIZEABLE (Level 3)All reads are consistent for the life of a transactionAll reads are consistent for the life of a transactionAvoids phantoms – no new recordsAvoids phantoms – no new records

Snapshot Isolation – 2005Snapshot Isolation – 2005 Transaction-Level consistency using snapshot Transaction-Level consistency using snapshot New non-blocking, non-locking, version-based New non-blocking, non-locking, version-based transactionstransactions

Transaction ManagerTransaction Manager

A Brief HistoryA Brief History

MTS 1.012/1996

DTC 1.04/1996

COM+ 1.012/1999

COM+ 1.58/2001

System.EnterpriseServices2/2002

WS-Transaction8/2002

MTS 2.012/1997

1996 1997 1998 1999 2000 2001 20021980 1990

IMS1973

CICS~1968

Encompass TandemACMS Digital

Mid 80’s

Tuxedo1984

Tandem TMF????

Encina1993

JTS12/1999

OMG OTS 1.25/2001

OASIS BTS5/2002

JTA4/1999

J2EE12/1999

BTS4/2000

1970

TIP 7/1998

OMG OTS 1.111/1997

XA (spec) 1991

Local TransactionsLocal Transactions

DBMSDBMS ApplicationApplication

ActivityActivity

ActivityActivity

ActivityActivity

ADOADOConnConn

Client 1Client 1

Client 2Client 2

Client NClient N

Transaction Transaction ManagerManager

LockLockManagerManager

DataData

VB VB ObjectObject

ADOADOConnConn

VB VB ObjectObject

ADOADOConnConn

VB VB ObjectObject

Distributed transactionDistributed transaction

Computer 3Computer 3

RM3 - ORACLERM3 - ORACLE

Participating DTCParticipating DTC

Computer 2Computer 2

RM2 -SQL ServerRM2 -SQL Server

Participating DTCParticipating DTC

Computer 1Computer 1

The Coordinating DTC The Coordinating DTC

RM1 - RM1 - MSMQMSMQDataData

DataData

Your Tx COM+ ApplicationYour Tx COM+ Application

QueueQueue

RM ProxyRM Proxy

RM ProxyRM ProxyRM ProxyRM Proxy

Two-Phase CommitTwo-Phase Commit

TransactionManager

ResourceManager

Prepare

Commit

Prepare and Force write “Prepared” record to RM log

Prepared

Force write “Commit” record to TM log

Lazy write “Committed” record to RM log and Release locks

CommittedLazy write “Committed”

record to TM log

Two Phase Commit – FailureTwo Phase Commit – Failure

TransactionManager

ResourceManager

Prepare

Commit

Prepare & Write “Prepared” record to

RM logPrepared

Write “Commit” record to TM log

Write “Committed” record to RM log &

Release locksCommitted

Write “Committed” record to TM log

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TodayTodayMS-DTCMS-DTC

APIAPIOLE TransactionsOLE Transactions

DTC ProxyDTC ProxyCOM InterfacesCOM Interfaces

App/TM, TM/RM, etcApp/TM, TM/RM, etcLocal or Remote TMLocal or Remote TM

API and configAPI and config

ProtocolsProtocolsOLE TransactionsOLE TransactionsXA, TIP, LU6.2XA, TIP, LU6.2

Resource ManagersResource ManagersSQL Server, MSMQSQL Server, MSMQDB2, Oracle, …DB2, Oracle, …

TodayTodayCOM+ TransactionsCOM+ Transactions

High Level Programming Model supporting High Level Programming Model supporting Declarative transaction modelDeclarative transaction modelProvides execution environment and full Provides execution environment and full support of all transaction features (e.g. support of all transaction features (e.g. commit coordination, isolation level, timeout, commit coordination, isolation level, timeout, etc.)etc.)Support for Compensating Resource Support for Compensating Resource Managers (CRM)Managers (CRM)Evolution of MTS (think MTS 3.0)Evolution of MTS (think MTS 3.0)Building Block for .Net Transaction ModelBuilding Block for .Net Transaction Model

TodayTodayTransaction ExampleTransaction Example

Transaction automatically createdTransaction automatically createdConnections automatically enlistedConnections automatically enlistedOutcome automatically coordinatedOutcome automatically coordinated

Root

Sub2Required or Requires New

RootClient

Sub1Sub1 & Sub 2 = Required orSupported

TransactionTransaction

TodayTodayTransactions in .NetTransactions in .Net

System.EnterpriseServices namespace System.EnterpriseServices namespace provides the programming modelprovides the programming modelAll COM+ features exposed via All COM+ features exposed via attributesattributesAll .Net language features availableAll .Net language features availableProvides full integration with the .Net Provides full integration with the .Net runtime integrationruntime integrationFull interop with existing COM+ Full interop with existing COM+ componentscomponents

TodayTodaySystem.EnterpriseServices ExampleSystem.EnterpriseServices Exampleusing System;using System;using System.Data.SqlClient;using System.Data.SqlClient;using System.EnterpriseServices;using System.EnterpriseServices;[assembly : ApplicationName("TxDemo")][assembly : ApplicationName("TxDemo")]  [Transaction(TransactionOption.RequiresNew, [Transaction(TransactionOption.RequiresNew,

Isolation = TransactionIsolationLevel.ReadCommitted, Isolation = TransactionIsolationLevel.ReadCommitted, Timeout = 60)]Timeout = 60)]

public class Account : ServicedComponentpublic class Account : ServicedComponent{{ [AutoComplete(true)][AutoComplete(true)] public void Credit()public void Credit() {{ // do some work// do some work }}}}

TomorrowTomorrow

New ArchitectureNew Architecture

System.Transaction

Lightweight Transaction Manager

(LTM)

DTC

Resource Manager

(SQL)

EnterpriseServices

Cross App DomainCross Computer

Lightweight Transaction Manager (LTM)Lightweight Transaction Manager (LTM)

Common Starting Point for TransactionsCommon Starting Point for TransactionsRemove any actual and perceived initial penalties for Remove any actual and perceived initial penalties for useuse

LTM is a full-fledged transaction manager for volatile LTM is a full-fledged transaction manager for volatile resourcesresources

Fast Transaction creationFast Transaction creationMinimum performance overhead when using volatile resource in Minimum performance overhead when using volatile resource in the same app-domainthe same app-domain

Promotable Single Phase Enlistment (PSPE) support to Promotable Single Phase Enlistment (PSPE) support to remove overhead when using a single resource managerremove overhead when using a single resource manager

In this case, the RM manages the transactionIn this case, the RM manages the transactionSingle log operationSingle log operation

Supported by SQL 2005Supported by SQL 2005Pay as you go – Dynamic PromotionsPay as you go – Dynamic Promotions

Application Usage ExampleApplication Usage ExampleUnify database and collection error handling:Unify database and collection error handling:

ImportsImports System.TransactionSystem.Transaction DimDim activeMembers activeMembers AsAs TransactedHashTable() TransactedHashTable()

Public SubPublic Sub AddMembership AddMembership ( (ByValByVal MemberName MemberName As StringAs String, _, _ ByValByVal Organization Organization As StringAs String))

UsingUsing ts ts As NewAs New TransactionScope() TransactionScope()

activeMembers.Add (MemberName, Organization)activeMembers.Add (MemberName, Organization) … … sqlCommand.ExecuteNonQuery (… add member insert…)sqlCommand.ExecuteNonQuery (… add member insert…) sqlCommand.ExecuteNonQuery (… add organization insert…)sqlCommand.ExecuteNonQuery (… add organization insert…) … … AppBizLogic = new AppBizLogicAppBizLogic = new AppBizLogic AppBizLogic.UpdateState(… state …)AppBizLogic.UpdateState(… state …) … … ts.Consistent = ts.Consistent = TrueTrue End UsingEnd Using

End SubEnd Sub

ArchitectureArchitecture

System.Transaction

Lightweight Transaction Manager

(LTM)

DTC

Resource Manager

(SQL)

EnterpriseServices

Cross App DomainCross Computer

IndigoService

Indigo TransactionIndigo TransactionService ModelService Model

Major Differences from Major Differences from COM+/EnterpriseServicesCOM+/EnterpriseServices

Transaction context does not flow by Transaction context does not flow by defaultdefaultTransaction flow is separate from Transaction flow is separate from transaction usagetransaction usageTransaction context is set at method Transaction context is set at method invocation, and not at object creation timeinvocation, and not at object creation time

Beyond IndigoBeyond IndigoTransacted Collection ClassesTransacted Collection ClassesLonghorn IntegrationLonghorn Integration

Kernel Transaction ManagerKernel Transaction ManagerTransacted File SystemTransacted File SystemTransacted RegistryTransacted Registry

Questions?Questions?

Further ReadingFurther ReadingPrinciples of Transaction ProcessingPrinciples of Transaction Processing

Bernstein and NewcomerBernstein and NewcomerTransactional COM+Transactional COM+

Tim EwaldTim EwaldSQL Server Architecture and InternalsSQL Server Architecture and Internals

Ken HendersonKen HendersonSQL Server 2005 for DevelopersSQL Server 2005 for Developers

Neils Burglend and Bob BeauchmenNeils Burglend and Bob BeauchmenProgramming IndigoProgramming Indigo

David PallmanDavid Pallman

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