External tables
Greenplum® allows you to work with data from sources that are external to a Managed Service for Greenplum® cluster. This functionality uses external tables, which are special objects in a Greenplum® database that reference external source tables, buckets, or files. Access to data in external DBMS's uses the Greenplum® Platform Extension Framework (PXF) protocol, whereas access to files on external file servers uses the Greenplum® Parallel File Server (gpfdist) utility.
With external tables, you can:
- Query external data sources.
- Load datasets from external sources into a Greenplum® database.
- Join local and external tables in queries.
- Write data to external tables or files.
Note
For security reasons, Managed Service for Greenplum® does not support the creation of external web tables that use shell scripts.
External data sources for PXF operations
Managed Service for Greenplum® uses external data sources to create external tables. Each source is similar to a web server configuration used to access data in external DBMS's. This is why sources are only used for PXF operations.
Sources enable you to do the following:
- In the configuration, specify the parameters that cannot be included in an SQL query for creating a PXF external table.
- Avoid explicitly specifying the user password in an SQL query for creating an external table.
- Simplify your SQL query for creating a table: with a dedicated source properly configured, there is no need to list configuration parameters in your query.
- Simplify your configuration update: it is enough to redefine the parameters at the source only once without changing them for each table separately.
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