1. Gert E.R. Drapers Software Architect Microsoft Corporation
8/2/2018 2:44 PM
DAT459 SQL Server And Distributed Transactions – Architecture And Internals
Gert E.R. Drapers
Software Architect
Microsoft Corporation
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

2. Agenda “Distributed” Transactions 101 Architecture Overview
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Agenda
“Distributed” Transactions 101
Architecture Overview
Client Initiated Distributed Transactions
Server Initiated Distributed Transactions
XA and JDBC integration
Oracle integration
Monitoring Distributed Transactions
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

3. Why Transactions? Correctness (programming model) ACID properties
8/2/2018 2:44 PM
Why Transactions?
Correctness (programming model)
ACID properties
Atomicity
All changes happen or nothing happens
Consistency
Data is transformed from one correct state to another
Isolation
Concurrent updaters are prevented from interfering with one another
Durability
Committed changes remain permanent despite failures
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

4. Roles Transaction System
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Roles 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 Manager
Controls changes to resources under the scope of a transaction
Uses a (durable) log for recovery
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

5. Isolation Goal: Maximize concurrency without unwanted interactions
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Isolation
Goal: Maximize concurrency without unwanted interactions
Higher isolation provides better consistency
Lower isolation provides better concurrency
Concurrency anomalies
Lost Updates (can overwrite uncommitted changes)
Dirty Reads (can read uncommitted changes)
Unrepeatable Reads (changing commits)
Phantoms (insert/delete anomalies)
DBMS defines its isolation rules
Read (shared) locks and write (exclusive) locks
Lock granularity: File, page, record, …
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

6. 8/2/2018 2:44 PM
Degrees of isolation
Whether or not these problems occur depends on a transaction’s degree of isolation
Degree 1 2
2.999 3
Common Name
Chaos
Read
Uncommitted
Read
Committed
Repeatable
Read
Serializable
A.K.A.
Browse
Cursor
Stability
Isolated
Lost Updates?
Yes No No No No
Dirty Reads?
Yes
Yes No No No
Unrepeatable Reads?
Yes
Yes
Yes No No
Phantoms?
Yes
Yes
Yes
Yes No
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

7. 8/2/2018 2:44 PM
Two-Phase Commit (2PC)
The two-phase commit protocol ensures that all transaction participants agree to either
Commit the transaction and make its effects permanent
Rollback the transaction and to undo its effects
It provides the “Atomicity” property of “ACID”
It is only needed when two or more parties participate in a transaction
Two-phase commit must work despite process, system, or communication failures
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

8. Two-Phase Commit Transaction Manager Resource Manager
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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
SQL
Server
Transaction
Manager
File
System
Resource
Managers
Resource Manager
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

9. Two-Phase Commit Transaction Manager Resource Manager Prepare
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Two-Phase Commit
Transaction
Manager
Resource
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
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

10. Two Phase Commit – Failure
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Two Phase Commit – Failure
Transaction
Manager
Resource
Manager
Abort on
Failure
Prepare
Abort on Failure
Prepare & Write “Prepared” record to RM log
Prepared
Will
Abort
Write “Commit” record to TM log
on Failure
Indoubt
Commit
Commit
Will
Write “Committed” record to RM log & Release locks
Commit
Committed
Write “Committed” record to TM log
Commit
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

11. MS-DTC Distributed Transaction Coordinator
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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, …
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

12. Local Transactions Data Client 1 Transaction Manager Lock Manager
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Local Transactions
Application
DBMS
Activity
VB Object
ADO
Conn
Client 1
Transaction Manager
Lock
Manager
Activity
ADO
Conn
Client 2
VB Object
Data
Activity
Client N
VB Object
ADO
Conn
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

13. Local Transactions All updates within a single DBMS
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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
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

14. Distributed Transactions
8/2/2018 2:44 PM
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
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

15. A Distributed Transaction
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A Distributed Transaction
Computer 2
RM2 -SQL Server
Participating DTC
Computer 1
The Coordinating DTC
RM1 - MSMQ
Data
Your Tx COM+ Application
RM Proxy
Queue
RM Proxy
RM Proxy
Computer 3
RM3 - ORACLE
Participating DTC
Data
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

16. SQL Server And Dist Tx Client initiated distributed transaction
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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
ITransactionJoin::JoinTransaction
ADO
Only implicit via MTS/COM+
System.Data.SqlClient
v1.0 only implicit via System.EnterpriseServices
v1.1 SqlConnection.EnlistDistributedTransaction
DB-Library – dbenlisttrans
MTS, COM+, System.EnterpriseServices
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

17. 8/2/2018 2:44 PM
OLE Transactions
Used by application programmers and resource manager developers
ITransactionDispenser is used to initiate transactions
ITransaction is used to commit or abort transactions
OLE Transactions
MS DTC implements the OLE Transactions standard
OLE Transactions describes the interfaces between transactional applications, transaction coordinators, and transactional resource managers
It defines the interfaces which transactional applications invoke to begin, commit, and abort distributed transactions.
It defines the interfaces implemented and used by transactional resource managers such as SQL Server to perform two-phase commit.
It defines the role of the transaction manager (coordinator) in guaranteeing atomic transaction outcome.
Model Summary
The application calls DtcGetTransactionManager to connect to MS DTC. DtcGetTransactionManager returns a pointer to the ITransactionDispenser interface.
The application invokes ITransactionDispenser::BeginTransaction and obtains a transaction object which represents the transaction.
The application associates the transaction with the ODBC or DB-Library connections to the SQL Server database.
For DB-Library connections, the application calls dbenlistxact for each connection.
For ODBC connections, the application calls SQLSetConnectOption for each connection
Each of the SQL Server’s enlists on the MS DTC transaction
The application then updates, inserts, or deletes records in one or more SQL Server databases.
The application calls ITransaction::Commit on the transaction object
MS DTC uses the two phase commit protocol to coordinate the transaction outcome with all of the enlisted SQL Server databases.
Normally, the transaction commits.
If a failure occurs during the two phase commit protocol or if the application calls ITransaction::Abort on the transaction object, then the transaction is aborted and the effects of the transaction are undone from all of the SQL Server databases.
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

18. SQL Server And Dist. Tx… Server initiated
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SQL Server And Dist. Tx…
Server initiated
BEGIN DISTRIBUTED TRANSACTION
Linked Server call
Extended Stored Procedures
srv_getdtcaxct NT
SQL
Server
MS DTC
Application
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

19. MS-DTC SQL Server Settings
8/2/2018 2:44 PM
MS-DTC SQL Server Settings
sp_configure “remote proc trans”, {0|1}
Server-wide option for automatically starting MS DTC transactions for server to server RPCs
SET REMOTE_PROC_TRANSACTIONS ON|OFF
Session-wide option for automatically starting MS DTC transactions for server to server RPCs
sp_configure “remote conn timeout”, <n>
Timeout on server to server RPCs before automatically dropping the connection
Connection will only be closed if there is no MS DTC transaction active for the connection
Overview
SQL Server is capable of automatically initiating MS DTC transactions. This is controlled using either a SQL server level option or a SQL session level option.
SQL Server Option
This is a server wide option which controls the default setting of the session level option.
New sessions started after altering the server option will take the setting of the server level option.
sp_configure “remote proc trans”, {0|1}
SQLSession Option
When the session level option is ON, SQL automatically initiates an MS DTC transaction whenever a remote stored procedure is invoked.
The value of the session option can be controlled using the the SET statement. SET REMOTE_PROCEDURE_TRANSACTIONS {ON|OFF}
The default value of the session level option is set based upon the value of the server wide option.
Timeout Option
SQL Server allows control of the timeout valuefor server to server RPC connections.
For high volumes of distributed transactions, a larger timeout period eliminates the need for constant re-establishment of server to server connections
The timeout period is configurable with a server configuration parameter:
sp_configure “remote conn timeout”, <n> where <n> specifies the timeout inactivity period, in minutes.
Connection will only be closed if there is no DTC transaction active for the connection.
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

20. Transact-SQL Explicit
8/2/2018 2:44 PM
Transact-SQL Explicit
BEGIN DISTRIBUTED TRANSACTION
This Transact-SQL call explicitly initiates an MS-DTC transaction
If a stored procedure calls a remote stored procedure, both stored procedures are protected by the MS-DTC transaction
Overview
Using MS DTC from SQL Server is very simple. An application can begin an MS DTC transaction explicitly using the Transact-SQL BEGIN DISTRIBUTED TRANSACTION statement. The COMMIT TRANSACTION or ROLLBACK TRANSACTION statements areused to commit or abort the MS DTC transaction.
Remote Stored Procedure Invocation
If a stored procedure running under the protection of an MS DTC transaction calls a remote stored procedure, the remote stored procedure will also run under the protection of the MS DTC transaction. If that remote stored procedure calls yet another remote stored procedure, it too will run under the protection of the MS DTC transaction.
Failure to propagate an MS DTC transaction to a remote server will cause the entiretransaction to abort.
Savepoints
The existing SQL Server SAVE TRAN statement is unchanged. A rollback of an MS DTC transaction will take all servers back to the state they were in when the MS DTC transaction was started. An application can perform partial rollbacks to named savepoints on individual servers without affecting the MS DTC transaction.
BEGIN DISTRIBUTED TRANSACTION INSERT INTO ACCOUNTS VALUES (100,20) EXEC RMTBRANCH.ACCOUNTS.DBO.DEPOSIT 100,20
COMMIT TRANSACTION
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

21. Transact-SQL Implicit
8/2/2018 2:44 PM
Transact-SQL Implicit
SQL Server can implicitly initiate an MS-DTC transaction when one is needed
This is controlled using two SQL Server options
Session-level option SET REMOTE_PROC_TRANSACTIONS ON
Server-level option sp_configure “remote proc trans”, 1
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

22. X-Database Transactions
8/2/2018 2:44 PM
X-Database Transactions
Cross-database transactions on the same SQL Server
Operations between two or more database result in a internal distributed transaction
Does not require DTC
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

23. Client Two-Phase Commit
8/2/2018 2:44 PM
Client Two-Phase Commit
DB-Library-based
Should no longer be used
Does not scale
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

24. 8/2/2018 2:44 PM
XA Transactions
Transactions can be coordinated by an XA compliant TP Monitor: Tuxedo, TopEnd, Encina, etc.
SQL Server can act as an XA compliant resource manager
Other XA compliant databases can be updated in the same transaction NT
NT or UNIX
SQL
Server
Application
TP Monitor
MS DTC
Oracle
Sybase
Informix XA
OLE Tx
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

25. 8/2/2018 2:44 PM
JDBC XA Integration
Microsoft JDBC driver can enlist SQL Server in an Java originated JTA transaction
By default not enabled, need to run INSTJDBC.SQL script to register
xp_jdbc_open, xp_jdbc_close, xp_jdbc_start, xp_jdbc_end, xp_jdbc_prepare, xp_jdbc_commit, xp_jdbc_rollback, xp_jdbc_forget, xp_jdbc_recover
Located in: C:\Program Files\Microsoft SQL Server 2000 Driver for JDBC\SQLServer JTA
Relies on XA switch library
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

26. Oracle Integration Oracle 7.x relies on MTXOCI.DLL
8/2/2018 2:44 PM
Oracle Integration
Oracle 7.x relies on MTXOCI.DLL
Oracle 8i, 9i and 10g should be using the Oracle provided DTC integration plumbing, named “Oracle Services for MTS”
No need to use MTXOCI8.DLL
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

27. Oracle Integration… 8/2/2018 2:44 PM
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

28. Transaction Monitoring
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Transaction Monitoring
SQL Server Trace/Profiler
DTCTransaction event class (19)
EventSubClass, BinaryData, TextData
SQLTransaction event class (50)
EventSubClass, TransactionID, ObjectName, TextData
Performance Monitor
Distributed Transaction Coordinator
Aborted Transactions
Aborted Transactions/sec
Active Transactions
Active Transactions Maximum
Committed Transactions
Committed Transactions/sec
Force Aborted Transactions
Force Committed Transactions
In Doubt Transactions
Response Time – Average
Response Time – Maximum
Response Time – Minimum
Transactions/sec
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

29. Transaction Monitoring…
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Transaction Monitoring…
DTC Trace
%windir%\system32\msdtc\trace\ msdtcvtr.bat
Requires TRACEFMT.EXE (Platform SDK)
Component Services
A.k.a., COM+ Explorer
MTS Spy/COM+ Spy
Platform SDK
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

30. MS-DTC Log Sizing Rules: How many concurrent transactions?
8/2/2018 2:44 PM
MS-DTC Log Sizing
Rules:
Log Record ~144 bytes (depends on number of RM’s involved in transaction)
MS-DTC uses a circular transaction log
Default Log Size is 4MB
DTC start rejecting new transactions when the current log space used is larger than the total Log Size / 8
How many concurrent transactions?
4MB / 144 bytes = 30000tx / 8 = ~ 3640 concurrent tx
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

31. Troubleshooting MS-DTC
8/2/2018 2:44 PM
Troubleshooting MS-DTC
Setup (reinstall)
Q – HOWTO: Reinstall MS DTC for a Nonclustered Windows NT 4.0 Server
Q – HOWTO: Reinstall MS DTC for a Nonclustered Windows 2000 Server
Communication
DTCPING (see Q306843)
Firewall
Q HOWTO: Troubleshoot MS DTC Firewall Issues
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

32. SQL Server ResourceMgrID
8/2/2018 2:44 PM
SQL Server ResourceMgrID
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\MSSQLServer
REG_SZ ResourceMgrID
GUID that UNIQUELY identifies this SQL Server instance
Reason for SQL Server SYSPREP or images based installs to fail
Needs to be duplicated on cluster nodes, otherwise transactions can not recover!
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

33. Information Q306843 HOWTO: Troubleshoot MS DTC Firewall Issues
8/2/2018 2:44 PM
Information
Q HOWTO: Troubleshoot MS DTC Firewall Issues
Q INFO: Names and IP Addresses an MS DTC Client Must Have
Q HOWTO: Set Up a Local MS DTC to Point to a Remote MS DTC
Q INFO: Log Files Used by Distributed Transaction Coordinator
Q MS DTC Leaks Handles If There Is Long String in TIP Transaction (Windows 2000 post service pack 2 hotfix rollup 19)
Q How to Troubleshoot MSDTC Event ID 4209
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

34. 8/2/2018 2:44 PM
Information…
Q INFO: Two-Phase Commit is Not Supported over TCP/IP for DB2OLEDB
Q HOWTO: Avoid COM/MTS Object Activation Delay on MSCS
Q MSDTC Disaster Recovery Techniques
Q INFO: The "msdtc -remove" Command Shows Errors
Q INFO: COM+ and MTS Always Use SERIALIZABLE Transaction Isolation
Q INF: Limited Support for Savepoint in Distributed Transactions
Q BUG: DTC Transactions Fail When SQL Runs in Lightweight Pooling
Q INF: FAQs – SQL Server 7.0 – FailoveR
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

35. Please fill out a session evaluation on CommNet
8/2/2018 2:44 PM
Please fill out a session evaluation on CommNet
Q1: Overall satisfaction with the session
Q2: Usefulness of the information
Q3: Presenter’s knowledge of the subject
Q4: Presenter’s presentation skills
Q5: Effectiveness of the presentation
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

36. Discussion E-Mail: gertd@microsoft.com http://SQLDev.Net
8/2/2018 2:44 PM
Discussion
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

37. © 2004 Microsoft Corporation. All rights reserved.
8/2/2018 2:44 PM
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.