Open topic with navigation
Virtual databases in DAH control mappings between the DAH and specific databases in child servers. When you query the DAH, you can use the
DatabaseMatch parameter to match a specific DAH virtual database (VDB), which in turn maps to databases in the child servers.
A VDB configuration might be useful in a complicated DAH environment, where you have mirror and non-mirror servers, and databases in different child servers might have different names.
When you create a VDB, you configure a name, and a list of databases that the VDB maps to. You can map a VDB to multiple databases from a single child server, and to databases from different child servers. See Example: Virtual Databases
The type of VDB defines whether DAH must treat the mapped databases as mirrors.
Combinator VDBs act in non-mirror mode, while
Distributor VDBs act in mirror mode.
You can configure VDBs to map to other VDBs in the same DAH. These are called recursive VDBs. It is sometimes better to replace recursive VDBs with actual DAH servers in a multiple DAH structure. See Advanced DAH Structures.