Resolving "Unrecognized Configuration Parameter" Errors After a Database Downgrade

Products

• VMware Tanzu Data Intelligence

Issue/Introduction

Issue Summary

When downgrading a database to an older version, users may encounter a login error with the following:

ERROR: unrecognized configuration parameter "<parameter_name>"

 

Cause

Root Cause

This issue occurs when a parameter—introduced in the newer database version—is applied at the Database or Role level and is not cleared before downgrading.

Because these settings persist in the system catalogs, the older database engine attempts to apply them during the connection initialization. Since the older version does not recognize the new GUC (e.g., a parameter like optimizer_enable_predicate_pushdown_below_view in 6.31.2 but not in 6.28), it throws an error when starting the client connection.

 

Resolution

Best Practice: Preventative Action

To avoid this issue entirely, it is highly recommended to reset any version-specific GUCs before initiating a downgrade.

While the system is still running on the newer version, you can simply use below command to reset DB level or ROLE level settings:

• ALTER DATABASE <db_name> RESET <new_parameter_name>;

• ALTER ROLE <role_name> RESET <new_parameter_name>;

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Workaround: Fixing the Error After Downgrade

If the database has already been downgraded, we cannot simply run a command to turn the parameter "off" (the older database engine will reject the command because the parameter name is unrecognized).

Instead, we must use the RESET ALL workaround to wipe the entity's configuration and reapply the valid settings.

Step 1: Identify Where the Setting is Applied

Run the following queries to determine if the unrecognized parameter is tied to a Database or a Role.

Check the Database level:

SELECT d.datname, s.setconfig
FROM pg_db_role_setting s
JOIN pg_database d ON s.setdatabase = d.oid 
WHERE setconfig::text ~ '<parameter_name>';

Check the Role level:

SELECT rolname, rolconfig 
FROM pg_roles 
WHERE rolconfig::text ~ '<parameter_name>';

Step 2: Back Up Existing Valid Settings

Before resetting, note the other valid settings so you can restore them later. Use the output from the queries in Step 1 to document the configurations.

Step 3: Reset All Configurations

Depending on where the setting was applied, run the appropriate RESET ALL command. This clears the unrecognized GUC from the system catalogs, resolving the login error.

If applied at the Database level:

ALTER DATABASE <db_name> RESET ALL;

If applied at the Role level:

(Note: Run this using a different superuser account than the one being reset.)

ALTER ROLE <role_name> RESET ALL; 

Step 4: Reapply Valid Configurations

Manually add back the original settings you documented in Step 2, omitting the unrecognized parameter.

ALTER DATABASE <db_name> SET <valid_setting_1> = 'value1';
-- OR --
ALTER ROLE <role_name> SET <valid_setting_1> = 'value1';

Validation: Once completed, test logging into the database using the affected role or database.