Example: Virtual Databases
A DAH has three child servers:
-
server 0 has a database of dog information, called
dogs
. -
server 1 has:
- a database of cat information, called
cats
. - a database of parrot information, called
parrots
.
- a database of cat information, called
-
server 2 has a database of flower information, called
flowers
.
Configuration
The following DAH VDB configuration queries all information about pets:
[VDB0] Name=pets MapsTo=0:dogs,1:cats,1:parrots Type=combinator
In this example, note that:
-
You do not have to reference all child servers in the
MapsTo
parameter. -
You can reference the same child server multiple times.
Query
When DAH receives a query with DatabaseMatch
set to pets
, DAH sends:
-
the query with
DatabaseMatch
set todogs
to server 0. -
the query with
DatabaseMatch
set tocats+parrots
to server 1.TIP: There are other advanced distribution options for VDBs, such as multi-stage querying. For more information, refer to the DAH Reference.