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. External DBMS data is accessed via the Greenplum® Platform Extension Framework (PXF) protocol; files on external file servers are accessed via 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.

External data sources for PXF operationsExternal 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.

Use casesUse cases

• Creating an external table from a Yandex Object Storage bucket table using a configuration file

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