How to fix 38000: external_routine_exception in PostgreSQL

Examine the PostgreSQL error logs and stack trace to identify which external function is failing. Look for function names in the error message or stack trace. You can also query the system catalogs:

SELECT proname, prolang, prosrc 
FROM pg_proc 
WHERE proname LIKE '%function_name%' 
  AND prolang IN (SELECT oid FROM pg_language WHERE lanname IN ('c', 'plpythonu', 'plperl', etc.));

Check for functions with LANGUAGE C or other external languages that might be causing the issue.

Verify that all extensions and external libraries are compatible with your PostgreSQL version. Check:

SELECT name, default_version, installed_version 
FROM pg_available_extensions 
WHERE installed_version IS NOT NULL;

Also check shared library dependencies:

# For Linux systems
ldd $(pg_config --pkglibdir)/*.so | grep -i "not found"

Ensure all required libraries are installed and compatible.

If you have access to the source code of the failing external routine:
1. Add logging or debugging statements to identify where it fails
2. Check for memory management issues (malloc/free mismatches)
3. Validate all input parameters and boundary conditions
4. Ensure exception handling is properly implemented

For C functions, compile with debugging symbols:

gcc -g -fPIC -shared -I$(pg_config --includedir-server) -o myfunc.so myfunc.c

Use tools like gdb or valgrind to debug memory issues.

Create a minimal test case to reproduce the error:

-- Test the function with simple inputs
BEGIN;
SELECT my_external_function('test_input');
ROLLBACK;

Gradually add complexity to identify what triggers the failure. Check:
- Input data types and values
- Memory usage patterns
- Concurrency issues (if multiple sessions call the function)
- Resource limits (memory, file descriptors)

Enable detailed logging in the external routine if possible.

Based on your debugging results:
1. Fix the bug in the external routine code
2. Add proper error handling and validation
3. Implement resource cleanup in all code paths
4. Add input validation to prevent invalid states

If you cannot fix the external routine, consider:
- Using a different function or extension
- Implementing the logic in PL/pgSQL instead
- Creating a wrapper function with error handling
- Reporting the bug to the extension maintainer

Example wrapper function:

CREATE OR REPLACE FUNCTION safe_external_function(input text)
RETURNS text
LANGUAGE plpgsql
AS $$
BEGIN
  BEGIN
    RETURN external_function_that_might_fail(input);
  EXCEPTION 
    WHEN external_routine_exception THEN
      RETURN 'Error: External routine failed';
  END;
END;
$$;

Implement monitoring and preventive measures:
1. Add comprehensive unit tests for external routines
2. Monitor PostgreSQL logs for external routine exceptions
3. Implement circuit breakers for frequently failing external functions
4. Consider using PostgreSQL's built-in languages (PL/pgSQL) when possible
5. Regularly update extensions and external libraries

Set up alerting for external routine failures:

-- Create a function to log external routine failures
CREATE OR REPLACE FUNCTION log_external_routine_failure(
  func_name text, 
  error_text text
) RETURNS void
LANGUAGE plpgsql
AS $$
BEGIN
  INSERT INTO external_routine_errors (function_name, error_message, occurred_at)
  VALUES (func_name, error_text, NOW());
END;
$$;