3.18. Foreign-data wrappers

Foreign-data wrappers are objects used to consume data from different data sources not necessarily another PostgreSQL database system. These different data sources can be CSV files, web services, or even database servers from different vendors.

Attributes	Description
Handler	The name of a previously registered function that will be called to retrieve the execution functions for foreign tables. The handler function must take no arguments, and its return type must be fdw_handler.
Validator	The name of a previously registered function that will be called to check the generic options given to the foreign-data wrapper, as well as options for foreign servers, user mappings, and foreign tables using the foreign-data wrapper.
Options	Specifies the options for the foreign-data wrapper. The allowed option names and values are specific to each foreign data wrapper and are validated using the foreign-data wrapper's validator function.

References

Foreign-data wrapper DDL

https://www.postgresql.org/docs/current/sql-createforeigndatawrapper.html