External tables

Greenplum® allows you to work with data from sources that are external to a 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

Yandex MPP Analytics for PostgreSQL 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
• Getting data from external sources using named queries

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