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PostgreSQL HV091 Error: Causes and Solutions Complete Guide

#postgres #database #dba #sql

PostgreSQL Error HV091: fdw_invalid_descriptor_field_identifier

PostgreSQL error HV091 (fdw_invalid_descriptor_field_identifier) occurs when a Foreign Data Wrapper (FDW) receives or uses an invalid field identifier while accessing a descriptor — a metadata structure used to describe columns and their attributes. This typically surfaces in custom FDW implementations, misconfigured foreign tables, or version mismatches between the FDW extension and PostgreSQL engine.

Top 3 Causes

1. Mismatched Foreign Table Column Definitions

When the column names or types defined in CREATE FOREIGN TABLE don't match the actual remote source schema, the FDW can fail to map descriptor fields correctly.

-- Problematic definition (wrong column name)
CREATE FOREIGN TABLE orders_foreign (
    id       INTEGER,
    customer TEXT,    -- remote column is actually 'cust_name'
    amount   NUMERIC
)
SERVER remote_pg_server
OPTIONS (schema_name 'public', table_name 'orders');

-- Fix: explicitly map remote column names using OPTIONS
DROP FOREIGN TABLE IF EXISTS orders_foreign;

CREATE FOREIGN TABLE orders_foreign (
    id       INTEGER OPTIONS (column_name 'order_id'),
    customer TEXT    OPTIONS (column_name 'cust_name'),
    amount   NUMERIC OPTIONS (column_name 'total_amount')
)
SERVER remote_pg_server
OPTIONS (schema_name 'public', table_name 'orders');

-- Best practice: use IMPORT FOREIGN SCHEMA to auto-sync
IMPORT FOREIGN SCHEMA public
    LIMIT TO (orders)
    FROM SERVER remote_pg_server
    INTO public;
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2. Invalid ODBC Descriptor Field Identifier in FDW Code

When using ODBC-based FDWs (odbc_fdw), passing an unsupported or incorrect FieldIdentifier constant to SQLGetDescField or SQLSetDescField triggers HV091. This often happens when custom FDW C code references wrong ODBC constants or uses deprecated API values.

-- Check current ODBC FDW server options
SELECT srvname, srvoptions
FROM pg_foreign_server
WHERE srvname = 'odbc_server';

-- Reconfigure with correct driver options
ALTER SERVER odbc_server OPTIONS (
    SET odbc_DRIVER 'PostgreSQL Unicode',
    SET odbc_SERVER 'remote_host',
    SET odbc_PORT   '5432',
    SET odbc_DATABASE 'targetdb'
);

-- Verify user mapping
SELECT usename, umoptions
FROM pg_user_mappings
WHERE srvname = 'odbc_server';

-- Test connection
SELECT * FROM orders_foreign LIMIT 5;
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3. FDW Extension and PostgreSQL Version Incompatibility

Upgrading PostgreSQL without updating FDW extensions (or vice versa) can cause internal API mismatches where descriptor field constants no longer align between the engine and the extension.

-- Check installed PostgreSQL version and FDW extensions
SELECT version();

SELECT e.extname,
       e.extversion,
       x.default_version AS latest_version,
       CASE
           WHEN e.extversion <> x.default_version THEN 'UPDATE REQUIRED'
           ELSE 'OK'
       END AS status
FROM pg_extension e
JOIN pg_available_extensions x ON e.extname = x.name
WHERE e.extname ILIKE '%fdw%';

-- Reinstall FDW extension to resolve version mismatch
DROP EXTENSION IF EXISTS mysql_fdw CASCADE;
CREATE EXTENSION mysql_fdw;

-- Recreate foreign server after reinstall
CREATE SERVER mysql_server
    FOREIGN DATA WRAPPER mysql_fdw
    OPTIONS (host '127.0.0.1', port '3306');
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Quick Fix Checklist

  1. Verify column mapping — Always use OPTIONS (column_name '...') to explicitly map foreign table columns to remote column names.
  2. Use IMPORT FOREIGN SCHEMA — Let PostgreSQL auto-generate foreign table definitions instead of writing them manually.
  3. Check extension versions — Run the version status query above after any PostgreSQL upgrade.
  4. Review FDW logs — Set log_min_messages = DEBUG1 temporarily to capture FDW-level descriptor errors. 
-- Enable detailed FDW logging for diagnosis
SET log_min_messages = DEBUG1;
SET client_min_messages = DEBUG1;

-- Re-run the failing query to capture descriptor details
SELECT * FROM your_foreign_table LIMIT 1;

-- Reset after diagnosis
RESET log_min_messages;
RESET client_min_messages;
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Prevention Tips

  • Automate schema sync: Schedule periodic IMPORT FOREIGN SCHEMA calls via pg_cron or an external cron job to keep foreign table definitions in sync with the remote source schema automatically.
  • Version-lock FDW extensions in CI/CD: Include FDW extension version checks in your deployment pipeline. Always test FDW compatibility in a staging environment before applying PostgreSQL major version upgrades to production.

Related Errors

Error Code Name Description
HV000 fdw_error Generic FDW error — parent class of HV091
HV005 fdw_column_name_not_found Column not found in remote source
HV009 fdw_invalid_use_of_null_pointer NULL pointer misuse in FDW implementation
HV00R fdw_unable_to_establish_connection Remote connection failure

📖 Want a more detailed guide?
Check out the full in-depth version (Korean) on oraerror.com — includes detailed analysis, additional SQL examples, and prevention tips.

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