How to diagnose and fix the HV002 fdw_dynamic_parameter_value_needed error code in Postgres.

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The HV002 error code in PostgreSQL indicates that a dynamic parameter value is needed by a foreign data wrapper (FDW). This situation can arise when a foreign table is defined with parameters that need to be dynamically set at runtime, but they have not been provided or are incorrectly set. To diagnose and fix this issue, you will need to ensure that all required parameters are correctly provided when the foreign table is queried.

Here are some examples and sample code to explain and address the possibilities that might trigger the HV002 error code:

Example 1: Missing Runtime Parameters

When creating a foreign table that requires runtime parameters, you must specify these parameters in your query. If you forget to include them, you will get the HV002 error.

-- Define the foreign table
CREATE FOREIGN TABLE my_foreign_table (
    ...
) SERVER my_foreign_server
OPTIONS (param1 'value1', ...);

-- Query that causes HV002 because it lacks required runtime parameters
SELECT * FROM my_foreign_table;

To fix this, include the required runtime parameters in the OPTIONS clause of your query:

-- Corrected query with runtime parameters
SELECT * FROM my_foreign_table OPTIONS (param1 'new_value1', ...);

Example 2: Incorrect Parameter Values

If you provide a parameter value that is not expected by the FDW, it may raise the HV002 error.

-- Query with an incorrect parameter value
SELECT * FROM my_foreign_table OPTIONS (param1 'incorrect_value', ...);

To resolve this, ensure that the parameter values match what the FDW is expecting:

-- Corrected query with proper parameter values
SELECT * FROM my_foreign_table OPTIONS (param1 'correct_value', ...);

Example 3: Using FDW Functions

Some FDWs provide functions to set or modify runtime parameters. If these functions are not used correctly, it could result in an HV002 error.

-- Incorrect use of a hypothetical FDW function that sets parameters
SELECT set_fdw_param('param1', 'value1');
SELECT * FROM my_foreign_table;

To fix this, make sure to use the FDW functions as intended, which might involve checking the FDW documentation or ensuring the function is executed in the correct context.

-- Correct use of the FDW function
BEGIN;
SELECT set_fdw_param('param1', 'value1');
SELECT * FROM my_foreign_table;
COMMIT;

When dealing with HV002 errors, always refer to the documentation of the specific FDW you are using, as the required parameters and their usage can vary significantly between different FDWs. The PostgreSQL documentation provides a list of error codes, but for specific FDW behavior, you will need to consult the documentation for the FDW itself or any related extensions you are using.

Remember, the key to resolving HV002 errors is to ensure that all required dynamic parameters are provided and used correctly according to the FDW’s specifications. If after these checks the issue persists, consider reaching out to the community or support resources for the specific FDW for further assistance.

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