PostgreSQL raises HV000 whenever a Foreign Data Wrapper fails but the connector cannot classify the failure into a narrower SQLSTATE. It usually hides a remote service error, driver mismatch, or a network hiccup, so you need to follow the FDW logs both in PostgreSQL and on the foreign system to find the root cause.
The error code appendix marks HV000 as the generic SQL/MED state labeled `fdw_error`, which FDWs emit when they catch a condition that does not match a more specific SQLSTATE. Because the foreign wrapper API hands control back to PostgreSQL before the remote log is shipped over, HV000 often means the remote database rejected the query, the FDW extension crashed, or the connector saw an unexpected response. Real-world support threads echo this: Supabase's Snowflake wrapper returns `ERROR: HV000: guest fdw error: expected value at line 1 column 1` when the remote service rejects the generated SQL, yet PostgreSQL only surfaces the generic HV000 message. The real failure lives entirely on the remote side, so the trick is tracing the SQL, payload, or authentication handshake that caused the wrapper to fall back to `fdw_error`.
Enable verbose logging on the Postgres side so you can see the exact statement the FDW uses and any additional error details:
1. Set the client log level to at least LOG:
SET client_min_messages = 'LOG';
SET log_min_error_statement = 'ERROR';
ALTER SYSTEM SET log_error_verbosity = 'verbose';
SELECT pg_reload_conf();2. If you are using postgres_fdw, also set the per-foreign-server log level:
ALTER SERVER my_remote FOREIGN DATA WRAPPER postgres_fdw OPTIONS (SET log_min_messages 'log');
ALTER SERVER my_remote FOREIGN DATA WRAPPER postgres_fdw OPTIONS (SET log_min_error_statement 'error');When HV000 fires again, the Postgres log will now show the SQL that hit the wrapper and any errors that you can correlate with the remote system.
Run these psql meta-commands to inspect the FDW configuration:
\des+
\dew+
\drds+ -- show foreign tables and serversCheck that the server host, port, database, and wrapper name match the remote system. Examine the user mapping for correct credentials, and look for options such as updatable, schema, table_name, or JSON settings that the wrapper expects.
Invalid or missing options cause the FDW to build SQL that the remote driver rejects with HV000, so a careful audit lets you rule out simple typos.
The supabase/wrappers issue for Snowflake shows the same HV000 pattern: the Postgres log only says ERROR: HV000: guest fdw error: expected value at line 1 column 1, but Snowflake never logs the query. Instead, reproduce the same foreign SQL using the remote client (Snowflake SQL editor, Oracle SQL*Plus, etc.), including any parameters sent by the FDW.
If the remote engine rejects the statement, its logs or client error message will explain whether the problem is malformed JSON, a missing column, or a permission denial. Fix the remote query, schema, or credentials so that the FDW stops hitting HV000.
Some wrappers add their own logging flags. For example, oracle_fdw can be built with debug prints, and JSON-based wrappers like Supabase’s can log the request payload before sending it over the wire. Enable those features or wrap the FDW in a trace logger so you can inspect the outbound payload.
If the remote side still reports nothing, consider enabling log_statement = 'all' temporarily; the goal is to capture the exact query/parameters that triggered HV000. Once you can observe both sides of the handshake, it usually reveals the real cause hidden behind the generic fdw_error.
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