xDB Reference Data database
Reference Data is common data referenced by data used across the Sitecore Experience Platform, for example while collecting, processing, or reporting. Examples are marketing taxonomies such as Campaigns, Goals, and Outcomes, as well as IP Geolocation or device information.
The Reference Data service and xDB Reference Data database is used to secure the integrity of data in the Sitecore Experience Database. It is a central store for data referenced throughout the Experience Platform processes, such as tracking, aggregation, and reporting.
Through the Sitecore management interface – for example through the Marketing Control Panel or the Campaign Management application - it is possible to create and update marketing metadata which can be associated with websites, pages, or actions on the web pages. This marketing metadata – for example, Goal or Campaign definitions, Marketing automation plan definitions, or taxonomies – are stored in the Master database. However, when the marketing metadata is ready for use, it needs to be deployed.
During the deployment, the Content Management role deploys the metadata to the Reference Data service, which in turn stores the data in the xDB Reference Data database. Storing the marketing metadata in the xDB Reference Data database means that the integrity of the data in the xDB is secured and that the deployed data can now be used by, for example, the aggregation process, marketing automation service, or in reporting.
The xDB Reference Data database contains marketing reference content for all xDB data, such as definitions and taxonomies.
The xDB Reference Data database is referenced by the following roles:
Contact data is not saved in the xDB Reference Data database.
Comparisons within the xDB Reference Data Database are case sensitive. Therefore, unlike other databases, the default collation of the xDB Reference Data database is set to Latin1_General_CS_AS.
Changing the default collation may result in definition key comparisons producing incorrect results. It is strongly recommended that you do not change the default collation.
xDB Collection database
The xDB Collection database(
sitecoreInsatnceName__Xdb.Collection.ShardMapManager) is likely to experience high read/write activity, and supports sharding. Experience data is sharded in the following way:
Contact and interaction data is sharded by contact ID.
The identifiers index is sharded by identifier.
Device profiles are sharded by device profile ID.
xConnect uses a change tracking functionality which requires a SQL User so it can access multiple databases. For this reason, contained database authentication cannot be used on the xDB Collection databases (shards and shard manager).
Reference: Why Xdb.Collection.Shard0, Xdb.Collection.Shard1 and Xdb.Collection.ShardMapManager databases in Sitecore 9 are not Partially Contained?