SQL Data Sync - Glossary of Terms

SQL Data Sync - Glossary of Terms

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This topic defines terms you need to know and understand when working with SQL Data Sync.

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This wiki topic is no longer updated by Microsoft. We moved the content to the MSDN Library where we keep it current.
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Client Sync Agent

The SQL Azure Client Sync Agent sits between the SQL Server database and the SQL Database hub database.
As part of the SQL Data Sync service the Client Sync Agent enables bi-directional HTTPS based communication between the on-premise SQL Server database and the SQL Database hub database.

Azure Sync Portal

The web UI that you use to interact with the Azure Sync Service.

Azure Sync Service

The backend SQL Data Sync Service running behind the Azure Sync Portal.


The dashboard gives you a high level overview of a particular SQL Data Sync server's status.
For example, how many sync groups and agents were created under this server, synchronization activity and status of each sync group and agent, entry to the log viewer, and so on.
This page allows you to do the first level of triage to understand your sync groups' overall health status.


A dataset is the collection of databases, tables, columns and optional rows (by filtering) that are synchronized each time a sync job is performed. The dataset is defined as you configure your sync group.

Force Removal

When a database is removed from a sync group in the normal fashion, it is de-provisioned for synchronization so that all the sync metadata is cleaned up from the database. However, if the de-provision operation fails for any reason, an error status on the database is displayed that this database failed to be removed from the sync group. You can then fix the issues that stopped the database from being de-provisoned automatically, for example, the network connection is down or the credential to the database is expired. If, for any reason, the de-provsion failure reason is unkown delete this database from the sync group by using the “Force Removal” link. This action may leave sync metadata behind inside your database and you may need to perform a manual clean up using the standalong tool that we provide to clean up the database. See the FAQ How do I manually deprovision my database for Sync?.

Hub Database

A hub database is the SQL Database that was defined as the "hub" when creating a Sync Group. 
In a Sync Group, SQL Databases that are not the hub are "member" databases. 
For each of the tables selected to participate in a Sync Group, the following steps occur every time a Sync Job is run:  1) changes in the member databases are uploaded to the hub database, and then 2) changes in the hub database are downloaded to the member databases.
After you deploy a sync group you cannot change which database is the hub database.

Member Database

A member database is any SQL Database that is part of the Sync Group and was not defined as the “hub” database by the user.
For more information on how member databases behave during synchronization, see the definition for “Hub Database.”
For more information on how member databases behave during a synchronization conflict, see the definition for “Synchronization Conflict.”
A member database can be added to or removed from a sync group any time the sync group is not in a synchronization session.

SQL Data Sync Preview

The current version of SQL Data Sync.

Sync Group

A Sync Group is a collection of SQL Database and SQL Server databases that are configured  for mutual synchronization by the SQL Data Sync service.
A Sync Group is comprised of a "hub" database and one or more "member" databases. 
The "hub" database must be a SQL Database. 
See Create Sync Group for a walk-through on creating a Sync Group.

Sync Job

A Sync Job is a scheduled synchronization task that can be added to the Sync Job Schedule, which defines the interval at which scheduled synchronizations are run. When a Sync Job is run synchronization is executed among the databases in the job's associated Sync Group.

Sync Loop

A Sync Loop occurs when one sync group's sync triggers the sync of another sync group in a circular fashion. This becomes an infinite loop of synchronizations which can so consume your resources that you cannot even bring up the Data Sync portal page. For information on the causes and cures of a sync loop see Sync Loop in the Troubleshooting Guide.

Synchronization Conflict

A synchronization conflict occurs when changes are made to the same piece of data in two or more databases between synchronizations.  The synchronization attempts to apply the changes into a single database.  In SQL Data Sync Preview you select the conflic resolution policy as you configure the sync group.
See SQL Data Sync: Collisions and Collision Resolution for a fuller explanation.


SQL Data Sync supports a hub-spoke topology with the SQL Database hub database as the bub and the other databases, SQL Database and SQL Server, as the spokes.
Thus SQL Data Sync supports cloud-to-cloud synchronizations as well as synchronizations involving both cloud and on-premises SQL Server databases.


This release was provided in order to gather feedback from our customers. Now that you have previewed what the SQL Data Sync team is doing, please let us know what you think of our direction, and tell us about your experiences.
You can send us your thoughts in any of the following ways:

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