PostgreSQL fdw_error (SQLSTATE HV000) Explained

What is PostgreSQL fdw_error (SQLSTATE HV000)?

PostgreSQL throws fdw_error when a Foreign Data Wrapper (FDW) encounters a problem it cannot classify into a more specific SQLSTATE. The error carries the condition name fdw_error and the code HV000.

The event typically appears while running SELECT, INSERT, UPDATE, or DELETE statements against foreign tables mapped to remote databases, files, or APIs.

Fixing it is crucial because the failure blocks data access paths that may be critical for application workflows.

What Causes This Error?

PostgreSQL surfaces fdw_error for any unhandled exception inside the FDW handler. Network drops, authentication failures, invalid option values, or bugs in the wrapper code all bubble up as HV000.

The error may also arise when the remote source returns malformed data, incompatible column types, or syntax the wrapper cannot translate.

For user written FDWs, missing error handling can convert a runtime fault into fdw_error.

How to Fix fdw_error

Start by isolating the failing foreign table and statement. Enable verbose logging (log_min_messages = DEBUG1) to capture the FDW’s internal message. Verify remote host reachability, credentials, and SSL settings.

Next, inspect FDW options with \det+ or by querying pg_foreign_table. Correct misspelled or unsupported options, then reload or ALTER FOREIGN TABLE to apply changes.

Finally, upgrade the FDW extension to the newest compatible version to pick up bug fixes.

Common Scenarios and Solutions

Network Timeout – Reconfigure tcp_keepalives or VPN rules and retry the query.

Changed Remote Schema – Refresh foreign table definitions with IMPORT FOREIGN SCHEMA or run ALTER FOREIGN TABLE.

Wrong Data Type Mapping – Cast columns in the SELECT or define column options (fdw_attname, fdw_type) to align types.

Best Practices to Avoid This Error

Keep FDW extensions patched and aligned with your PostgreSQL version.

Use connection pooling like pgBouncer to stabilize links to remote servers.

Monitor pg_stat_foreign_tables and PostgreSQL logs for early warning signs. Wrap custom FDW code with explicit exception handling to emit precise SQLSTATEs.

Related Errors and Solutions

HV005 fdw_schema_not_found signals a missing remote schema. Run IMPORT FOREIGN SCHEMA or adjust search_path.

42804 datatype_mismatch arises when column casts are incompatible. Cast or alter column types to match.

57P01 admin_shutdown occurs if the remote server closes the session.

Check remote server uptime and restart the query.

.