Sqlpass The Magic Of Replication

The Magic of Replication

What’s new in SQL Server 2008 Replication?

Who Am I?

Meir Dudai• SQL Server consultant – Valinor (SQL Server

Consulting Services)• Working with SQL Server for 10 years• Specialize in Replication, my favorite feature in

SQL Server• Operating SQL Server Israeli website:

http://www.SQLServer.co.il/

meir@valinor.co.il

Agenda

• SQL Server’s greatest challenge• Replication overview• Peer-to-Peer Replication • Replication enhancements – SQL Server 2008

SQL Server’s greatest challenge

SQL Server’s greatest challenge

• We want availability and scalability!• The database is a

single point of failure

• The database sometimes is the performance bottleneck

Scale UpScale

Out

A DBA’s dream

• Application/website always online• Workload is distributed amongst many servers

Scalability and Availability Options in SQL Server

•Copy unreadableDatabase Mirroring

•Read only•Restores prevent online activity and vice versa

Log Shipping

•Read only•High latency

Backup/Restore

Scalability and Availability Options in SQL Server

•High latency•Requires development effortsSSIS

•A mythScalable Shared Databases

•…Replication

Agenda

• SQL Server’s greatest challenge• Replication overview• Peer-to-Peer Replication • Replication enhancements – SQL Server 2008

What is Replication?

• “Make copies of digital material for backup, performance, reliability, or preservation”

(Digital Libraries, by William Arms)

• “The use of redundant resources to improve reliability, fault-tolerance, or performance “ (Wikipedia)

How does it work?

Create a full copy

Identify changes on source (Publisher)

Store changes into distribution database

Distribute changes to destination (subscriber)

Agenda

• SQL Server’s greatest challenge• Replication overview• Peer-to-Peer Replication • Replication enhancements – SQL Server 2008

Introduction to Peer-to-Peer Replication

• Databases replicate

reciprocally and are writable

• Redundancy provides fault

tolerance and lowers

maintenance downtime

• Online upgrades possible

Peer-to-Peer Topology

Distribution Agent

DistDB

Logreader Agent

Distribution Agent

DistDB

Logreader Agent

Los Angeles London

Taipei

Transactional Replication

Distribution Agent

DistDB

Logreader Agent

Peer-to-Peer– common scenarios

• Scale out reads and writes

or…

• Scale out reads, but writes are done to one node only

Peer-to-Peer – Multisite solution?

Back to the DBA’s dream:Peer-to-Peer Replication!• Application/website always online• Workload is distributed amongst many servers

Implementing Peer-to-Peer

Challenges

• Design your schema and topology properly to prevent conflicts

• P2P is an asynchronous solution and does not guarantee zero data loss or zero latency

• Not completely transparent• Although transparent enough!

Agenda

• SQL Server’s greatest challenge• Replication overview• Peer-to-Peer Replication • Replication enhancements in

SQL Server 2008

Changing replication topology online

• In SQL Server 2005, replication had to be stopped (quiesced) in order to perform some actions:• Add nodes• Schema changes

• In SQL Server 2008, these actions can be done online

• And you also get a cool wizard in SSMS…

Configure Peer-to-Peer Topology Wizard

Demo

Conflict Detection and Resolution

• SQL Server 2008 introduces

conflict detection capability in

peer-to-peer replication

• All types of conflicts are detected

and reported though agent error

reporting or conflict tables

• Two options on detecting conflict

• Fail replication stream

• Continue stream after

logging conflict

Update tbl_user set Name =‘cameron’

Update tbl_user set Name =‘camern’

Conflict Detection and Resolution

• Conflicts are resolved based on

originator_id value – higher wins

• Manual resolution of conflicts is

required in most cases

• Best approach: Prevent

conflicts through write

partitioning even with conflict

detection capabilities availableUpdate tbl_user set Name =‘cameron’

Update tbl_user set Name =‘camern’

Enabling Conflict Detection

• Enable conflict detection

in publication properties

• Set a value for the

originator ID

• Specify action in case of

conflict:

• Stop and alert (default)

• Continue (may cause data inconsistency)

Viewing conflicts

• When a conflict occurs, replication will stop by default

• You can view the conflict using Conflict Viewer in SSMS and address it manually

Conflict Detection and Resolution

Demo

Replicating partition switch

• In SQL Server 2005, switch partition action was unsupported in replicated environment

• This was a major consideration for organizations when deciding whether to use replication or not

• In SQL Server 2008, you can switch partition on a replicated table, and replicate this action

• Requires some settings in publication properties

Replicating partition switch

• Publication properties:• @allow_partition_switch: allows SWITCH PARTITION

to be executed against the publication database• @replicate_partition_switch: determines whether the

SWITCH PARTITION DDL statement should be replicated to Subscribers

• Preparations:• Make sure that all tables that are involved in partition

switching exist at the Publisher and Subscriber• Make sure that the table and partition definitions are the

same

• Switch partition using ALTER TABLE command

Performance improvements

• Under Windows Server 2008, replication works faster than ever:• Snapshot delivery of more than 500MB/minute• One of the interesting benchmarks for a pull

subscriber, time to deliver 100,000 varbinary (max) records:

• Win2003/SQL2005 – 223 minutes

• Win2008/SQL2008 – less than 2 minutes!

Conclusion

• Peer-to-Peer Replication can provide one of the best methods for systems scale out• Dramatically increase performance• Eliminate downtime

• SQL Server 2008 provides major improvements for Peer-to-Peer Replication, and makes it accessible and more robust

Related sessions

• Building a High Availability Strategy for your Enterprise

Gopal Ashok

Wednesday, 10:15AM

• Transactional Replication: Beyond The Basics

Kendal Van Dyke

Thursday, 4:00PM

Q&A

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