- Babelfish for Aurora PotgreSQL : Single -Mode versus Multiple - mode ?   This will impact how many user Database can co-exist on a single Babelfish Instance . 

To illustrate the point , If you're accessing a Babelfish for Aurora PostgreSQL in  single-mode , you will be able to have a single user database , if you attempt to create more than 1 database , the following message will appear 

Only one user database allowed under single-db mode. User database "xxxxxxx" already exists

Single-Mode considerations

            - can only create 1 t-sql database in Babelfish 

             - schemas are created as regular PostgreSQL schemas in Babelfish database

             -  The other impact is that the  SQL Server Schema Names Remain the same in the babelfish db. The schema names remain the same as in SQL Server.  From a migration perspective this makes it straightforward. If you were using    dbo and myschename1 in SQL Server , the same references will apply in Babelfish 

Multiple-Mode considerations

      -  can create multiple t-sql databases (with a unique set of schemas per database)

      - a t-sql schema is created as PostgreSQL schema for name conflict 

        -  In comparison to single mode , if you were to configure Babelfish as  multiple mode , although you will see the schema names through SQL Server as the same , they will be referenced as dbname_schemaname  when viewed through PostgreSQL.   So if you  have a database called   - myDB1  with   myschema1 and myschema2   , when it's migrated to Babelfish , from a SQL Server perspective the references remain the same.      But through PostgreSQL    the schema reference  become    myDB1_myschema1 and myDB1_myschema2

The migration-mode  (single or multiple) is stored in the migration-mode parameter. Once you've set it and built the Babelfish instance it isn't possible to change it 

By default - it's set at single mode

How can you check the current migration mode on an AWS Babelfish for Aurora PostgreSQL?

Using the Amazon RDS interface  => Go to the Parameter groups and find the relevant Parameter Group for the Babelfish instance. Click on the Parameter Group and search for the "migration mode" parameter  . The current value will be in the Values column 

Read more on Babelfish for Aurora PotgreSQL

    Spotlight on Babelfish for Aurora PostgreSQL