Module 4:Implementing Transactional Replication

Overview

Understanding Transactional Replication Architecture

Replicating with Transactional Replication

Implementing Updatable Transactional Replication

Facilitating Transactional Replication by Using Stored Procedures

Troubleshooting Transactional Replication

Tuning Transactional Replication

Lesson: Understanding Transactional Replication Architecture

How Transactional Replication Moves Data

The Role of the Log Reader Agent

How the Log Reader Agent Reads the Transaction Log

How the Log Reader Agent Changes Transaction Syntax

The Role of the Distribution Agent

Independent and Shared Agents

Concurrent Snapshot Generation

How Transactional Replication Moves Data

Snapshot ensures synchronized table schema and dataSnapshot ensures synchronized table schema and data

Log Reader Agent scans transaction logLog Reader Agent scans transaction log

Log Reader Agent copies transactions marked for replication to DistributorLog Reader Agent copies transactions marked for replication to Distributor

Distribution Agent moves transactions from Distributor to SubscribersDistribution Agent moves transactions from Distributor to Subscribers

The Role of the Log Reader Agent

1111 The Log Reader Agent is created when the first transactional publication is created on the Publisher

Log Reader Log Reader AgentAgent

Log Reader Log Reader AgentAgentCreatedCreatedCreatedCreated2222 The Log Reader Agent looks

in the distribution database for the last LSN read

Each time the Log Reader Agent runs:

3333 The Log Reader Agent reads the transaction log of the publishing database starting with the next LSN

distributiondistribution

LSN: 18

Transaction log

Transaction log

1111 The Log Reader Agent is created when the first transactional publication is created on the Publisher

Log Reader Log Reader AgentAgent

Log Reader Log Reader AgentAgent

2222 The Log Reader Agent looks in the distribution database for the last LSN read

Each time the Log Reader Agent runs:

3333 The Log Reader Agent reads the transaction log of the publication database starting with the next LSN

distributiondistribution

LSN: 18

Transaction log

Transaction log

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How the Log Reader Agent Reads the Transaction Log

1111 Finds the next LSN

2222 Starts reading transactions

3333 Ignores transactions related to nonpublished objects

4444 Copies the published transactions to the distribution database

5555 Marks the log as transactions read to here

LSN:************** 29: XXXXX

LSN:************** 17: UPDATELSN:************** 18: XXXXX LSN:************** 19: UPDATE LSN:************** 20: UPDATE LSN:************** 21: INSERTLSN:************** 22: DELETELSN:************** 23: UPDATELSN:************** 24: INSERTLSN:************** 25: INSERTLSN:************** 26: UPDATE LSN:************** 27: INSERT LSN:************** 28: INSERT

UPDATEUPDATEINSERTUPDATE …

6666 Anything prior to the mark can be truncated

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How the Log Reader Agent Changes Transaction Syntax

INSERT INTO Emp VALUES (57, 'Bremer', 'Ted') INSERT INTO Emp VALUES (57, 'Bremer', 'Ted')

CALL sp_MSins_Emp (57, 'Bremer', 'Ted') CALL sp_MSins_Emp (57, 'Bremer', 'Ted') May convert to astored procedureMay convert to astored procedure

UPDATE XYZ SET …UPDATE XYZ SET …

DELETE XYZ …INSERT XYZ …

DELETE XYZ …INSERT XYZ …

May convert to anDELETE/INSERT

May convert to anDELETE/INSERT

UPDATE Emp SET Phone = '5559521' WHERE LastName = 'Bremer' AND FirstName = 'Ted'

UPDATE Emp SET Phone = '5559521' WHERE LastName = 'Bremer' AND FirstName = 'Ted'

CALL sp_MSupd_Emp (57, '5559521') CALL sp_MSupd_Emp (57, '5559521') Uses primary keyUses primary key

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The Role of the Distribution Agent

distribution database

distribution database

subscribing database

subscribing database

subscribing database

subscribing database

Distribution Distribution AgentAgent

Distribution Distribution AgentAgent

DTSPackage

DTSDTSData PumpData Pump

DTSDTSData PumpData Pump

Transformable subscriptions only

Transformable subscriptions only

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subscribing database

subscribing database

subscribing database

subscribing database

Independent and Shared Agents

Shared Agent

Shared Agent

Independent Agent

Independent Agent

Independent Agent

Independent Agent

Concurrent Snapshot Generation

Marks the log

Copies the tables

Marks the log

Checks the log between the marks for transactions marked for replication

Applies the initial snapshot

Applies the transactions copied from the marked portion of the log

Publishing Database

Transaction log

Transaction log

INSERT…X

Subscribing Database

Tablesprocsviews

Tablesprocsviews

Distributor

SQLSQL

1111

2222

3333

4444

5555

6666

X

INSERT…

INSERT…

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Lesson: Replicating with Transactional Replication

Designing Tables for Transactional Replication

Replicating text, ntext, and image Data

Replicating Horizontally Filtered Data

Overhead of Filtering for Transactional Replication

Designing Tables for Transactional Replication

Y Related row

INSERT X, Y, Z

Insert on Publisher checks the relationship

Insert on Publisher checks the relationship

It is not necessary to check again on the Subscriber

It is not necessary to check again on the Subscriber

ReplicationReplicationReplicationReplication

ReplicationReplicationReplicationReplication

Use NOT FOR REPLICATION for relationshipsUse NOT FOR REPLICATION for relationshipsUse NOT FOR REPLICATION for relationshipsUse NOT FOR REPLICATION for relationships

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Y Related row

INSERT X, Y, Z

Practice: Designing Tables for Transactional Replication

Adding syntax

ALTER TABLE and CLUSTERED INDEX

ALTER TABLE and FOREIGN KEY

CREATE TRIGGER

Replicating text, ntext, and image Data

Reinitialize the publication if nonlogged operations have occurred

Use the WITH LOG option with text operations

Use max text repl size with ODBC subscribers

Replicating Horizontally Filtered Data

CREATE PROCEDURE CustFilter FOR REPLICATION ASIF EXISTS ( SELECT Country FROM Customers WHERE Country IN (SELECT Country FROM Promotion (NOLOCK)) RETURN 1ELSE RETURN 0

CREATE PROCEDURE CustFilter FOR REPLICATION ASIF EXISTS ( SELECT Country FROM Customers WHERE Country IN (SELECT Country FROM Promotion (NOLOCK)) RETURN 1ELSE RETURN 0

Overhead of Filtering in Transactional Replication

Number of filters

Every row tested against every filter

Each filter is evaluated independently

Complexity

Complexity determines overhead

Joins, functions, comparisons, and indexes contribute to overhead

Lesson: Implementing Updatable Transactional Replication

What Are Updating Subscriptions?

Limitations of Updating Subscriptions

How Subscribers Using Immediate Updating Subscriptions Update Tables

Schema Alterations for Subscribers Using Immediate Updating Subscriptions

Choosing a Queue Type

How Queued Updating Subscriptions Update Tables (SQL Server 2000 queue)

How Queued Updating Subscriptions Update Tables (MSMQ)

Managing Conflicts with Subscribers Using Queued Updating Subscriptions

Implementing Immediate Updating with Failover to Queued Updating

Managing Identity Values for Updating Subscriptions

Subscriber using immediate updating

subscription

Subscriber using queued

updating subscription

What Are Updating Subscriptions?

Publisher

Distributor

Queue Reader Agent

Reliable Connection

Reliable Connection

Queue

IntermittentConnectionIntermittentConnection

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Limitations of Updating Subscriptions

No merge replication

No republishing replicated data at the Subscriber

All text and image data should be treated as read-only

Cannot disable the updating subscription

Cannot use INSERT statements without a column list

Cannot combine with transformable subscriptions

Cannot use pre-existing data at Subscribers

How Subscribers Using Immediate Updating Subscriptions Update Tables

Publisher updates table and forwards transactionsPublisher updates table and forwards transactions

Subscriber starts transaction and connects with MS DTCSubscriber starts transaction and connects with MS DTC

MS DTC completes data modification with two-phase commit (2PC)MS DTC completes data modification with two-phase commit (2PC)

Publisher distributes update to other Subscribers according to schedulePublisher distributes update to other Subscribers according to schedule

Schema Alterations for Subscribers Using Immediate Updating Subscriptions

MSrepl_tran_version

Added by wizard if needed

Include vertical filter

Add to column list

System-defined triggers

Added automatically when subscribers enabled

Make calls to MS DTC

Avoiding a trigger-firing loop

Fire user-defined triggers after immediate updating triggers

Choosing a Queue Type

SQL Server 2000 queue

Works with all SQL Server platforms

Easy to set up

No additional components to install

Faster

Microsoft Message Queue (MSMQ)

Centralized queue administration and monitoring

Propagate changes when Subscriber is not running SQL Server

Does not require available Publisher when Subscriber reconnects

Publisher updates table and forwards transactions using typical transactional replicationPublisher updates table and forwards transactions using typical transactional replication

Subscriber trigger places copy of new transactions in MSreplication_queueSubscriber trigger places copy of new transactions in MSreplication_queue

SQL Server Queue Reader Agent checks for new rows to be moved to Distributor queueSQL Server Queue Reader Agent checks for new rows to be moved to Distributor queue

SQL Server Queue Reader Agent uses MS DTC to move rows to PublisherSQL Server Queue Reader Agent uses MS DTC to move rows to Publisher

Publisher distributes update to other SubscribersPublisher distributes update to other Subscribers

SQL Server 2000 Queue:SQL Server 2000 Queue:SQL Server 2000 Queue:SQL Server 2000 Queue:

How Queued Updating Subscriptions Update Tables (SQL Server 2000 Queue)

Publisher updates table and forwards transactions using typical transactional replicationPublisher updates table and forwards transactions using typical transactional replication

MSMQ places transaction in MSMQ-managed queueMSMQ places transaction in MSMQ-managed queue

MSMQ service on Subscriber moves row to MSMQ service on Distributor by using MS DTCMSMQ service on Subscriber moves row to MSMQ service on Distributor by using MS DTC

MSMQ service on Distributor connects to Publisher and updates Subscriber table by using MS DTCMSMQ service on Distributor connects to Publisher and updates Subscriber table by using MS DTC

Publisher distributes update to other SubscribersPublisher distributes update to other Subscribers

MSMQ:MSMQ:MSMQ:MSMQ:

How Queued Updating Subscriptions Update Tables (MSMQ)

Managing Conflicts with Subscribers Using Queued Updating Subscriptions

How SQL Server detects conflicts

Choosing a conflict resolver

Keep change made at Publisher

Keep change made at Subscriber

Reinitialize the subscription

Implementing Immediate Updating with Failover to Queued Updating

Immediate updatingImmediate updatingImmediate updatingImmediate updating

1111 Using immediate updating

2222 Connection is unavailable

3333 Switch to queuing

4444 When connection is available – empty the queue

5555 Resume immediate updating

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QueueQueue1.

2.

3.

4.

4. 3. 2. 1. 4. 3. 2. 1.

Managing Identity Values for Updating Subscriptions

Methods for managing identity values

Use SQL Server 2000 automatic management Use the NOT FOR REPLICATION option Use a primary key other than the identity column

Identity values and immediate updating

Publisher controls identity values You cannot assign identity ranges

Identity values and queued updating

Assigned by the Subscriber Identity values and queued updating failover

Assign identity ranges to Subscribers Inserted rows generate identity values from the range

Lesson: Facilitating Transactional Replication by Using Stored Procedures

Understanding Custom Stored Procedures for Replication

Creating Custom Stored Procedures

Implementing Custom Stored Procedures

Understanding Custom Stored Procedures for Replication

Benefits of custom stored procedures

Improved performance Less data passed over the network

Command types

CALL MCALL XCALL SQL NONE

Creating Custom Stored Procedures

sp_scriptinsproc

sp_scriptdelproc

sp_scriptupdproc

sp_scriptmappedupdproc

sp_scriptdynamicupdproc

sp_scriptpublicationcustomprocs

Implementing Custom Stored Procedures

Lesson: Troubleshooting Transactional Replication

Troubleshooting by Using the Distribution and Log Reader Agents

Troubleshooting by Using Stored Procedures

Skipping Errors to Prevent Replication Halts

Reinitializing Subscriptions

Troubleshooting Steps

Troubleshooting Guidelines

Troubleshooting by Using the Distribution and Log Reader Agents

"C:\Program Files\Microsoft SQL Server\80\COM\logread" -Publisher [VANCOUVER] -PublisherDB [Northwind] -DistributorSecurityMode 1

"C:\Program Files\Microsoft SQL Server\80\COM\logread" -Publisher [VANCOUVER] -PublisherDB [Northwind] -DistributorSecurityMode 1

"C:\Program Files\Microsoft SQL Server\80\COM\distrib" -Publisher [VANCOUVER] -PublisherDB [Northwind] -Publication [CustomersTransactional] -DistributorSecurityMode 1

"C:\Program Files\Microsoft SQL Server\80\COM\distrib" -Publisher [VANCOUVER] -PublisherDB [Northwind] -Publication [CustomersTransactional] -DistributorSecurityMode 1

Log Reader AgentLog Reader AgentLog Reader AgentLog Reader Agent

Distribution AgentDistribution AgentDistribution AgentDistribution Agent

Troubleshooting by Using Stored Procedures

sp_browsereplcmds – Commands waiting at Distributor

sp_replshowcmds – Commands waiting at Publisher

sp_repltrans – LSNs in transaction log

sp_replflush – Stop acting as the Log Reader Agent

sp_repldone – System use only

sp_replqueuemonitor – Lists queue messages

DBCC OPENTRAN – Returns oldest LSNs

sp_replcmds – System use only

Practice: Troubleshooting by Using Stored Procedures

Create a push subscription and subscribe

Identify commands at Distributor

Identify commands at Publisher

Skipping Errors to Prevent Replication Halts

Reinitializing Subscriptions

Troubleshooting Steps

Check Replication Monitor

Change -BatchCommitSize

Disable Cleanup

Rerun distribution

Check MSreplication_subscriptions

Identify the row

Narrow the query

Map the sequence number

Display commands

Troubleshooting Guidelines

Use SQL error logs

Run DBCC checks

Check for blocking issues

Analyze index and query performance on subscribing tables

View application and System Event Viewer logs

Check triggers

Lesson: Tuning Transactional Replication

Identifying Subscriber Factors That Degrade Performance

Improving Performance Through Design and Configuration

Improving Performance by Using Appropriate Subscription Types and Scheduling

Improving Performance by Using Agent Properties

Identifying Subscriber Factors That Degrade Performance

Subscriber computer factors

Subscription database or SQL Server setup factors

Network speed or connection factors

Additional factors

Improving Performance Through Design and Configuration

Design factors

Use custom stored procedures

Avoid individual row evaluation

Publish as indexed views instead of filtered tables

Avoid the update of unique constrained columns

Configuration factors

Set the distribution database to a fixed size

Configure the Distributor on a dedicated server

Improving Performance by Using Appropriate Subscription Types and Scheduling

Subscription factors

Use push and pull subscriptions appropriately

Use anonymous subscriptions appropriately

Scheduling factors

Run agents continuously

Reduce distribution frequency

Schedule snapshots during periods of low activity

Improving Performance by Using Agent Properties

Property of both the Log Reader Agent and Distribution Agent

Use -PollingInterval parameter to adjust latency Log Reader Agent Properties

Increase -ReadBatchSize parameter Retain -ReadBatchThreshold default Adjust the -MaxCmdsInTran setting

Distribution Agent Properties

Increase -CommitBatchSize and -CommitBatchThreshold defaults

Review

Understanding Transactional Replication Architecture

Replicating with Transactional Replication

Implementing Updatable Transactional Replication

Facilitating Transactional Replication by Using Stored Procedures

Troubleshooting Transactional Replication

Tuning Transactional Replication

Lab 4: Implementing Transactional Replication

Exercise 1: Designing a Transactional Replication Solution

Course Evaluation