Microsoft Fabric: Mirroring (Notes)

Disclaimer: This is work in progress intended to consolidate information from various sources.
Last updated: 18-Apr-2024

Mirroring in Microsoft Fabric (adapted after [2])

Mirroring

• low-cost, low-latency fully managed service that allows to replicate data from various systems together into OneLake [1]
• supported in Azure SQL Database, Azure Cosmos DB, Snowflake [1]
• ⇒ replaces ETL pipelines
• ⇐ manages the replication of data into OneLake and conversion to Parquet [1]
• changes have a near real-time latency [3]
• uses the source database’s CDC feature [4]
• {benefit} allows users to use a highly integrated, end-to-end, and easy-to-use service [1]
• the mirrored data can be used in Power BI
• ⇐ since tables are all v-ordered delta tables [3]
• {benefit} the delta tables can then be used in every Fabric experience, allowing users to accelerate their journey into Fabric [1]
• {restriction} replication of views is currently not supported [3]
• {benefit} allows to write cross-database queries against the mirrored databases, warehouses, and the SQL analytics endpoints of Lakehouses in a single T-SQL query [1]
• landing zone in OneLake 
• stores both the snapshot and change data [3]
• ⇐ improves performance when converting files into delta verti-parquet [3]
• {operation} enable the mirroring 
• by creating a secure connection to the operational data source
• an entire database or individual tables can be replicated 
• creates three items in the targeted workspace:
• the mirrored database
• a SQL analytics endpoint
• a Default semantic model
• the same source database can be mirrored multiple times
• ⇐ though usually not needed
• scenario: replicating data to different types of environments
• {operation} stopping the mirroring
• stops the replication in the source database, but a copy of the tables is kept in OneLake [3]
• {operation} restarting the mirroring 
• results in all data being replicated from the start [3]
• {operation} remove a table from mirroring
• the table is no longer replicated and its data is deleted from OneLake [3]
• {operation} sharing
• users grant other users or groups of users access to a mirrored database without giving access to the workspace and the rest of its items [1]
• access is also granted to the SQL analytics endpoint and associated default semantic model [1]
• shared mirrored databases can be found through either
• Data Hub
• Shared with Me section in Microsoft Fabric
• triggers an initial replication
• {requirement} [licensing] requires Power BI Premium, Fabric Capacity, or Trial Capacity
• {feature} monitoring
• {benefit} allows to gain insights into mirroring operations and when the replica in Fabric OneLake was last refreshed [4]
• [Azure SQL Database] 
• {restriction} doesn't support Azure SQL Database logical servers behind an AVN or private networking [2]
• {requirement} update the Azure SQL logical server firewall rules to Allow public network access [2]
• {requirement} enable the Allow Azure services option to connect to your Azure SQL Database logical server [2]
• {restriction}
•  access through the Power BI Gateway or behind a firewall is unsupported [3]
• authentication
• SQL authentication with user name and password
• Microsoft Entra ID
• Service Principal
• {troubleshooting} check if the changes properly flow
• via sys.dm_change_feed_log_scan_sessions DMV
• {troubleshooting} check if there are any problems reported
• via sys.dm_change_feed_errors DMV
• {troubleshooting} check if the mirroring was properly enabled
• via sp_help_change_feed stored procedure 
• {troubleshooting} disable mirroring
• via sp_change_feed_disable_db stored procedure

Acronyms:
AVN - Azure Virtual Network
CDC - Change Data Capture

ETL - Extract, Transfer, Load

DMV - Dynamic Management View

References:
[1] Microsoft Learn - Microsoft Fabric (2024) What is Mirroring in Fabric? (link)
[2] Microsoft Learn - Microsoft Fabric (2024) Mirroring Azure SQL Database [Preview] (link)
[3] Microsoft Learn - Microsoft Fabric (2024) Frequently asked questions for Mirroring Azure SQL Database in Microsoft Fabric [Preview] (link)
[4] Microsoft Fabric Updates Blog (2023) (link)

Resources:
[1] Tutorial: Configure Microsoft Fabric mirrored databases from Azure SQL Database [Preview] (link)
[2] Microsoft Fabric Updates Blog (2024) Announcing the Public Preview of Mirroring in Microsoft Fabric, by Charles Webb (link)