To utilize the Foreign Data Wrapper (FDW) feature in PostgreSQL, you need to install the relevant extension and execute setup commands, including creating foreign tables, servers, and user mappings. For detailed instructions, refer to the official PostgreSQL documentation.
Once the necessary settings are in place, the functions provided by the FDW extension come into play during query processing to access foreign tables.
Query Tree Creation:
The query analyzer (or analyser) constructs the query tree based on the input SQL statement.
Remote Server Connection:
The planner (or executor) establishes a connection with the remote server that hosts the foreign table.
Cost Estimation:
If the use_remote_estimate option is enabled (off by default), the planner executes EXPLAIN commands on the remote server to estimate the cost of various plan paths.
SQL Statement Generation:
The planner generates a plain text SQL statement from the plan tree, a process known as deparsing.
Remote Execution and Result Retrieval:
The executor sends the plain text SQL statement to the remote server for execution and retrieves the resulting data.
By following these steps, FDW allows PostgreSQL to seamlessly interact with foreign tables on remote servers. The performance of FDW queries depends on factors such as network latency, the efficiency of the foreign server, and the data volume being transferred.
PostgreSQL's FDW feature enables efficient access to and manipulation of foreign tables located on remote servers. By executing setup commands and leveraging the provided extension, you can seamlessly integrate remote data sources into your PostgreSQL database.
The performance of FDW queries involves steps such as query tree creation, remote server connection, cost estimation, SQL statement generation, and remote execution. Taking into account factors like network latency and server efficiency, FDW empowers PostgreSQL to process queries on foreign tables effectively.
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