SQL Server replication: Overview of components and topography

The volume of data retained, managed, and accessed today is unprecedented. Businesses expect the IT department to keep data online and accessible indefinitely, putting intense pressure on the databases required to store and manage it. To meet today’s needs; we need to replace outdated and inefficient legacy processes with new, more agile techniques. SQL Server Replication is one of the techniques to accommodate such demands.

In this article, let’s you shape your understanding of the full SQL Server replication topography including components, internals and the SQL to bind it all together. After you complete reading this article, you‘ll understand:

SQL Server replication, in general Components of transactional SQL Server replication, in particular How to get distributor properties How to find the publisher using the same distributor What are the databases used for SQL Server replication The general topology of a replication environment What are the articles that are mapped to the type of SQL Server replication model How to get publication details How to get subscription details SQL Server Replication agents And more… Replication

SQL Server replication is a technology for copying and distributing data and database objects from one database to another and then synchronizing between databases to maintain consistency and integrity of the data. In most cases, replication is a process of reproducing the data at the desired targets. SQL Server replication is used for copying and synchronizing data continuously or it can also be scheduled to run at predetermined intervals. There are several different replication techniques that support a variety of data synchronization approaches; one-way; one-to-many; many-to-one; and bi-directional, and keep several datasets in sync with each other.

Transactional SQL Server replication components

The following diagram depicts the components of transactional SQL Server replication.

Including the SQL Server replication …

Publisher Publication database Publication Articles Distributor Distribution database Subscriber Subscription database Subscription Replication agents

SQL Server replication diagram

Article

An article is the basic unit of SQL Server Replication. An article can consist of tables, stored procedures, and views. It is possible to scale the article, horizontally and vertically using a filter option. We can also create multiple articles on the same object with some restrictions and limitations.

Using the New Publication wizard, the Article can be navigated . It allows us to view the properties of an article and provide options to set properties for the articles. In some case, the properties can be set during the time of publication creation and it’s a read-only property.

After the creation of a SQL Server replication publication, for instance, if some property requires a change, it will, in turn, require a new replication snapshot to be generated. If the publication has one or more subscriptions then the change requires all subscriptions to be reinitialized. For more information, see How to add/drop articles to/from existing publication in SQL Server article .

To list all the articles that are published, run the following T-SQL

SELECT Pub.[publication][PublicationName] ,Art.[publisher_db] [DatabaseName] ,Art.[article][Article Name] ,Art.[source_owner] [Schema] ,Art.[source_object][Object] FROM [distribution].[dbo].[MSarticles]Art INNER JOIN [distribution].[dbo].[MSpublications] Pub ON Art.[publication_id] = Pub.[publication_id] ORDER BY Pub.[publication], Art.[article]

To get the details of articles in transactional or merge SQL Server replication in a published database, run the following T-SQL.

SELECT st.name [published object], st.schema_id, st.is_published , st.is_merge_published, is_schema_published FROM sys.tables st WHERE st.is_published = 1 or st.is_merge_published = 1 or st.is_schema_published = 1 UNION SELECT sp.name, sp.schema_id, 0, 0, sp.is_schema_published FROM sys.procedures sp WHERE sp.is_schema_published = 1 UNION SELECT sv.name, sv.schema_id, 0, 0, sv.is_schema_published FROM sys.views sv WHERE sv.is_schema_published = 1;

To get detailed information about an article in the listed publisher, run the following T-SQL

DECLARE @publication AS sysname; SET @publication = N'PROD_HIST_Pub'; USE MES_PROD_AP EXEC sp_helparticle @publication = @publication; GO

To get column level details, run the following T-SQL

USE MES_PROD_AP GO sp_helparticlecolumns@publication = N'PROD_HIST_Pub' ,@article ='tb_Branch_Plant'

To list the columns that are published in transactional replication in the publication database, run the following T-SQL

SELECT object_name(object_id) [published table], name [published column] FROM sys.columns sc WHERE sc.is_replicated = 1; Publications

A Publication is a logical collection of articles from a database. The entity allows us to define and configure article properties at the higher level so that the properties are inherited to all the articles in that group.

EXEC sp_helppublication; Publisher database

The publisher is a database that contains a list of objects that are designated as SQL Server replication articles are known as publication database . The publisher can have one or more publications. Each publisher defines a data propagation mechanism by creating several internal replication stored procedures.

USE Distribution GO select * from MSpublications

Publisher

The Publisher is a database instance that makes data available to other locations through SQL Server replication. The Publisher can have one or more publications, each defining a logically related set of objects and data to replicate.

Distributor

The Distributor is a database that acts as a storehouse for replication specific data associated with one or more Publishers. In many cases, the distributor is a single database that acts as both the Publisher and the Distributor. In the context of SQL Server replication, this is commonly known as a “local distributor”. On the other hand, if it’s configured on a separate server, then it is known as a “remote distributor”. Each Publisher is associated with a single database known as a “distribution database” aka the “Distributor”.

The distribution database identifies and stores SQL Server replication status data, metadata about the publication, and, in some cases, acts as a queue for data moving from the Publisher to the Subscribers.

Depending on the replication model, the Distributor might also be responsible for notifying the Subscribers that have subscribed to a publication that an article has changed. Also, the distribution database maintains the integrity of the data.

Distribution databases Each Distributor must have at least one distribution database. The distribution database consists of article detail, replicati