ptg This page intentionally left blank Download from www.wowebook.com ptg CHAPTER 19 Replication IN THIS CHAPTER . What’s New in Data Replication . What Is Replication? . The Publisher, Distributor, and Subscriber “Magazine” Metaphor . Replication Scenarios . Subscriptions . Replication Agents . Planning for SQL Server Data Replication . SQL Server Replication Types . Basing the Replication Design on User Requirements . Setting Up Replication . Scripting Replication . Monitoring Replication There is no such thing as a typical configuration or appli- cation anymore. Companies now have to support numerous hardware and software configurations in multitiered, distributed environments. These diverse configurations and applications (and users of the applications) come in all sizes and shapes. And, of course, you need a way to deal with varied data access requirements for these different physical locations; these remote or mobile users over a local area network, wide area network, wireless connections, and dial- up connections; and any needs over the Internet. Microsoft’s data replication facility allows for a great breadth of capability to deal with many of these demands. However, to build a proper data replication implementation that meets many of these user requirements, you must have a thorough understanding of the business requirements and technical capabilities of data replication. Data replication is a set of technologies for storing and forwarding data and database objects from one database to another and then synchronizing this data between databases to maintain consistency. With SQL Server 2008, the data replication feature set offers numerous improvements in manageability, availability, programmability, mobility, scalability, and performance. This chapter does the following: . Helps you understand what data replication is . Shows you how to understand and analyze user requirements of data . Allows you to choose which replication configuration best meets these requirements (if any) Download from www.wowebook.com ptg 546 CHAPTER 19 Replication . Demonstrates how to implement a replication configuration . Describes how to administer and monitor a data replication implementation What’s New in Data Replication Much of what’s new for Microsoft SQL Server data replication revolves around simplifying setup, administration, and monitoring of a data replication topology. This is the result of years of practical experience and thousands of production replication implementations around the globe. The overall data replication approach that Microsoft has developed (since replication’s inception back in SQL Server 6.5 days) has been so solid that competi- tors, such as Oracle (with its Oracle Streams technology), have tried to mimic this architec- tural approach. Among many others, the following are some of the new replications features and enhancements that make SQL Server 2008 data replication one of the best data distribu- tions tools on the market: . Highly available replication node additions—SQL Server 2008 offers the capa- bility to add nodes to a replication topology without quiescing the topology. . Topology Viewer—Enhancements have been made to the Peer-to-Peer Topology Wizard so that you can now visually see what the peer-to-peer topology looks like with the Topology Viewer. . Capability to centrally monitor all agents and jobs at the Publisher—You are able to view information about all the agents and jobs associated with publications at the selected Publisher. . Minor Replication Monitor enhancements—Replication Monitor has undergone slight tweaks to make it easier to monitor your full replication topologies. It allows you to monitor the overall health of a replication topology and provides detailed information about the status and performance of publications and subscriptions. . Capability to replicate switch partition ALTER—Enhanced Transactional Replication Support for Partitioned Tables is now available, including the capability to replicate the switch partition ALTER for Tables. . Scripting integrated into wizards—You can almost completely script your replica- tion setup or breakdown during or after wizard executions. . Conflict Viewer—This feature helps you view and resolve any conflicts that occurred during the synchronization of a merge subscription or queued updating subscription. . Peer-to-peer transactional replication—Further enhancements have been intro- duced to the peer-to-peer replication model. They allow replication between identi- cal participants in the topology (a master/master or symmetric publisher concept). . Peer-to-peer conflict detection—The capability to detect conflicts during synchro- nization in a peer-to-peer replication topology has been added. Download from www.wowebook.com ptg 547 What Is Replication? Insert “A” (Store) Distribute “A” (Forward) A A A A FIGURE 19.1 The store-and-forward data distribution model. . More replication mobility—Merge replication provides the capability to replicate data over HTTPS with the web synchronization option, which is useful for synchro- nizing data from mobile users over the Internet or synchronizing data between Microsoft SQL Server databases across a corporate firewall. . Microsoft Sync Framework—This comprehensive synchronization platform enables collaboration and offline access for applications, services, and devices. It fea- tures technologies and tools that enable roaming, sharing, and taking data offline. By using Sync Framework, developers can build sync ecosystems that integrate any application with any data from any store that uses any protocol over any network. We mention it here because of its replication-like behavior for “occasionally con- nected” applications. Many of these terms and references might be new or foreign to you now, but they are all explained in this chapter. At the end of this chapter, when you review these new features, you’ll be able to appreciate much more readily their significance. What Is Replication? Long before you ever start setting up and using SQL Server data replication, you need to have a solid grasp of what data replication is and how it can be used to meet your company’s needs. In its classic definition, data replication is based on the “store-and- forward” data distribution model, as shown in Figure 19.1. In other words, data that is inserted, updated, or deleted in one location (stored) is automatically distributed (forwarded) to one or more locations. 19 Of course, the data distribution model addresses all the other complexities of updates, deletes, data latency, autonomy, and so on. It is this data distribution model that Microsoft’s data replication facility serves to implement. It has come a long way since the early days of Microsoft SQL Server replication (earlier than 6.5) and is now easily catego- rized as “production worthy.” Numerous worldwide data replication scenarios have been implemented for some of the biggest companies in the world without a hitch. These scenarios fall into five major types: Download from www.wowebook.com ptg 548 SQL Server 2008 Primary OLTP Reporting/ODS OLTP DB SQL Server 2008 Reporting Server Rpt DB SQL Server 2008 North America Region Regionalization (multiple owners) xyz DB SQL Server 2008 Europe Region xyz DB SQL Server 2008 Primary Failover xyz DB SQL Server 2008 Hot Spare (Fail-over) xyz DB SQL Server 2008 USA (Headquarters) Enabling/Partitioning xyz DB SQL Server 2008 Europe Server xyz DB SQL Server 2008 Asia Server xyz DB FIGURE 19.2 Data replication scenarios. . Offloading—You might need to deliver data to different locations to eliminate network traffic and unnecessary load on a single server (for example, when you need to isolate reporting activity away from your online transaction processing). The industry trend is to create an operational data store (ODS) data architecture that replicates core transactional data to a separate platform in real-time and delivers the data to the reporting systems, web services, and other data consumers without impacting the transactional systems in any way. . Enabling—You might need to enable a group of users with a copy of data or a subset of data (vertically or horizontally) for their private use. . Partitioning—You might need to move data off a single server onto several other servers to provide for high availability and decentralization of data (or partitioning of data). This might be the basis of serving customer call centers around the globe that must service “active” support calls (partitioned on active versus closed service requests). . Regionalization—You might have regional ownership of data (for example, regional customers and their orders). In this case, it is possible to set up data replica- tion to replicate data bidirectionally from two or more publishers of the same data. . Failover—You could be replicating all data on a server to another server (that is, a failover server) so that if the primary server crashes, users can switch to the failover server quickly and continue to work with little downtime or data loss. Figure 19.2 illustrates the topology of some of these replication variations. CHAPTER 19 Replication Download from www.wowebook.com ptg 549 The Publisher, Distributor, and Subscriber Magazine Metaphor 19 As you may notice, you can use data replication for many reasons. Many of these reasons are discussed later in this chapter. First, however, you need to understand some of the common terms and metaphors Microsoft uses in relationship to data replication. They started with the “magazine” concept as the basis of the metaphor. A magazine is created by a publisher, distributed via the mail, and delivered to only those who have a subscrip- tion to the magazine. The frequency of the magazine publication can vary, as can the frequency of the subscription (depending on how often the subscriber wants to receive a new magazine). The publication (magazine) consists of one or more articles. One or more articles can be subscribed to. The Publisher, Distributor, and Subscriber Magazine Metaphor Any SQL Server can play up to three distinct roles in a data replication environment: . Publication server—The publication server (or publisher) contains the database or databases that will be published (the magazine!). This is the source of the data that is to be replicated to other servers. In Figure 19.3, the Customer table (an article in the magazine) in the AdventureWorks2008 database is the data to be published. To publish data, the database that contains the data that will be published must first be enabled for publishing. Full publishing configuration requirements are discussed later in this chapter, in the section “Setting Up Replication.” Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate SQL Server 2008 Publisher “Magazine” metaphor Adventure Works translog SQL Server 2008 Distributor distribution Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate SQL Server 2008 AdventureWorks Customer (Sales) Customer ID Territory ID AccountNumber Customer Type rowguid ModifiedDate SQL Server AdventureWorks Subscriber(s) FIGURE 19.3 The publisher, distributor, and one or more subscribers. Download from www.wowebook.com ptg 550 . Distribution server—The distribution server (or distributor) can either be on the same server as the publication server or on a different server (in which case it is a remote distribution server). This server contains the distribution database. This data- base, also called the store-and-forward database, holds all the data changes that are to be forwarded from the published database to any subscription servers that subscribe to the data. A single distribution server can support several publication servers. The distribution server is truly the workhorse of data replication; it is essen- tially the mail system that picks up the magazine and delivers it to the subscription holder. . Subscription server—The subscription server (or subscriber) contains a copy of the database or portions of the database being published (for example, the Customer table in the AdventureWorks2008 database). The distribution server sends any changes made to this table (in the published database) to the subscription server’s copy of the Customer table. This is known as store-and-forward. Some data replication configurations send the data to the subscription server, and then the data is read- only. It is also possible for subscribers (known as updating subscribers) to make updates, which are sent back to the publisher. More on this in the Updating Subscribers Replication Model section. There are now new variations of this update subscriber option called peer-to-peer replication. Peer-to-peer allows for more than one publisher of the same data (table) at the same time! Essentially, each publisher is also a subscriber at the same time (hence, peer-to-peer). This chapter provides more information on updating subscribers and peer-to-peer configura- tions in the “The Updating Subscribers Replication Model” section, later. Along with enabling distinct server roles (publisher, distributor, and subscriber), Microsoft utilizes a few more magazine metaphors, including publications and articles. A publication is a group of one or more articles and is the basic unit of data replication. An article is simply a pointer to a single table, or a subset of rows or columns out of a table, that will be made available for replication. Publications and Articles A single database can contain more than one publication. You can publish data from tables, from database objects, from the execution of stored procedures, and even from schema objects, such as referential integrity constraints, clustered indexes, nonclustered indexes, user triggers, extended properties, and collation. Regardless of what you plan to replicate, all articles in a publication are synchronized at the same time. Figure 19.4 shows an example of a publication (named Cust_Orders publication) with three articles (three tables from the AdventureWorks2008 database). You can also choose to replicate whole tables or just parts of tables via filtering. Filtering Articles You can create articles within a publication in several different ways. The basic way to create an article is to publish all the columns and rows contained in a table. Although this is the easiest way to create articles, your business needs might require that you publish only specific columns or certain rows of a table. This is referred to as filtering vertically or CHAPTER 19 Replication Download from www.wowebook.com ptg 551 SQL Server 2008 Publisher Publication Adventure Works translog Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate SalesOrderHeader (Sales) SalesOrderID RevisionNumber OrderDate DueDate ShipDate Status OnlineOrderFlag SalesOrderNumber PurchaseOrderNumber AccountNumber CustomerID ContactID SalesPersonID TerritoryID BillToAddressID ShipToAddressID ShipMethodID CreditCardID CreditCardApprovalCode CurrencyRateID SubTotal TaxAmt Freight TotalDue Comment rowguid ModifiedDate Cust_Orders Cust_Orders SalesOrderHeader (Article) SalesOrderDetail (Article) SalesOrderDetail (Sales) SalesOrderID SalesOrderDetailID CarrierTrackingNumber OrderQty ProductID SpecialOfferID UnitPrice UnitPriceDiscount LineTotal rowguid ModifiedDate FIGURE 19.4 The Cust_Orders publication (in the AdventureWorks2008 database). The Publisher, Distributor, and Subscriber Magazine Metaphor 19 horizontally. When you filter vertically, you filter only specific columns, whereas with hori- zontal filtering, you filter only specific rows. In addition, SQL Server 2008 provides the added functionality of join filters and dynamic filters. As Figure 19.5 shows, you might need to replicate only a customer’s CustomerID, TerritoryID, and CustomerType to various subscribing servers around your company. In your company, the other data, such as AccountNumber, may be restricted information that should not be replicated for general use. For that reason, you simply create an article for data replication that contains a subset of the Customer table that will be replicated to these other locations and excludes AccountNumber (and rowguid and ModifiedDate as well). As another example, you might need to publish only the Customer table data for a specific customer type, such as “individual” customers ((CustomerType = ‘I’) or customers that are “stores” (CustomerType = ‘S’). This process, as shown in Figure 19.6, is known as horizontal filtering. It is possible to combine horizontal and vertical filtering, as shown in Figure 19.7. This way, you can weed out unneeded columns and rows that aren’t required for replication (that is, are not needed by the subscribers). For example, you might need only the customers that are stores and need only CustomerID, TerritoryID, and CustomerType data to be published. Download from www.wowebook.com ptg 552 CHAPTER 19 Replication SQL Server 2008 Publisher Publication Adventure Works translog Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate AW_Vertical CustomerV (Article) 1345 1356 2354 3346 7643 7901 8921 1 2 1 2 3 5 4 AW1345 AW1356 AW2354 AW3346 AW7643 AW7901 AW8921 CustomerID 1345 1356 2354 3346 7643 7901 8921 ModifiedDate I I S I S I I CustomerTypeTerritoryID X69G9 W211G 7SQ78K W12DV WZ8R4 S2345X RT66Y rowguidAccountNumber 1345 1356 2354 3346 7643 7901 8921 1 2 1 2 3 5 4 CustomerID TerritoryID I I S I S I I CustomerType FIGURE 19.5 Vertical filtering creates a subset of columns from a table to be replicated to subscribers. SQL Server 2008 Publisher Publication Only these Rows! Adventure Works translog Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate AW_Horizontal CustomerH (Article) 1345 1356 2354 3346 7643 7901 8921 1 2 1 2 3 5 4 AW1345 AW1356 AW2354 AW3346 AW7643 AW7901 AW8921 CustomerID 120203 051605 106705 022305 122205 041506 0321206 ModifiedDate I I S I S I I CustomerTypeTerritoryID X69G9 W211G 7SQ78K W12DV WZ8R4 S2345X RT66Y rowguidAccountNumber 2354 7643 1 3 CustomerID TerritoryID AW2354 AW7643 106705 122205 ModifiedDate S S CustomerType 7SQ78K WZ8R4 rowguidAccountNumber FIGURE 19.6 Horizontal filtering creates a subset of rows from a table to be replicated to subscribers. Download from www.wowebook.com ptg 553 The Publisher, Distributor, and Subscriber Magazine Metaphor 19 SQL Server 2008 Publisher Publication Only these Columns and these Rows! Adventure Works translog Customer (Sales) CustomerID TerritoryID AccountNumber CustomerType rowguid ModifiedDate AW_H_and_V CustomerHV (Article) 1345 1356 2354 3346 7643 7901 8921 1 2 1 2 3 5 4 AW1345 AW1356 AW2354 AW3346 AW7643 AW7901 AW8921 CustomerID 120203 051605 106705 022305 122205 041506 0321206 ModifiedDate I I S I S I I CustomerTypeTerritoryID X69G9 W211G 7SQ78K W12DV WZ8R4 S2345X RT66Y rowguidAccountNumber 2354 7643 1 3 CustomerID TerritoryID S S CustomerType FIGURE 19.7 Combining horizontal and vertical filtering allows you to pare down the informa- tion in an article to only the important information needed by the subscribers. As mentioned earlier, it is now possible to use join filters. Join filters enable you to use the values of one article (that is, values from a table) to determine what gets replicated from another article (that is, what values can be associated with another table) via a join. In other words, if you are publishing the Customer table data based on the customers that are stores, you can extend filtering (that is, a join filter) to replicate only those orders for these types of customers (as shown in Figure 19.8). This way, you replicate only orders for customers that are stores to a subscriber that needs to see only this filtered data. This type of replication can be efficient if it is done well. You also can publish stored procedure executions, along with their parameters, as articles. This can be either a standard procedure execution article or a serializable procedure execu- tion article. The difference is that the latter is executed as a serializable transaction; the serializable option is recommended because it replicates the procedure execution only if the procedure is executed within the context of a serializable transaction. If that same stored procedure is executed from outside a serializable transaction, changes to data in published tables are replicated as a series of DML statements. In general, replicating stored procedure executions gives you a major reduction in the number of SQL statements being replicated across the network versus standard DML statements. Download from www.wowebook.com . DB SQL Server 2008 Primary Failover xyz DB SQL Server 2008 Hot Spare (Fail-over) xyz DB SQL Server 2008 USA (Headquarters) Enabling/Partitioning xyz DB SQL Server 2008 Europe Server xyz DB SQL. www.wowebook.com ptg 548 SQL Server 2008 Primary OLTP Reporting/ODS OLTP DB SQL Server 2008 Reporting Server Rpt DB SQL Server 2008 North America Region Regionalization (multiple owners) xyz DB SQL Server 2008 Europe. enhancements that make SQL Server 2008 data replication one of the best data distribu- tions tools on the market: . Highly available replication node additions SQL Server 2008 offers the capa- bility