Aurora Postgres 15.10 - Master Logs - displaying only parameter markers and not the actual values.

When you're seeing only parameter markers instead of actual values in your Aurora PostgreSQL 15.10 logs after a major upgrade, this is likely related to the parameter group settings, specifically those related to logging.

This behavior is often controlled by the pgaudit.log_parameter parameter. When this parameter is not enabled, PostgreSQL logs will show parameter markers (like $1, $2, etc.) instead of the actual parameter values in SQL statements.

To resolve this issue and see the actual parameter values in your logs, you should:

1. Check your current parameter settings by connecting to your PostgreSQL database and running:

SHOW pgaudit.log_parameter;

Or to see all parameters:

SHOW ALL;

2. If pgaudit.log_parameter is set to 'off' or not enabled, you'll need to modify your custom parameter group to enable it.

3. After upgrading to a new major version like 15.10, you need to ensure that your custom parameter groups are properly configured for the new version. During major version upgrades, you should create new custom parameter groups specific to the target version and apply your customizations there.

4. After modifying the parameter group, you may need to reboot your database instance for the changes to take effect. The parameter group status will show "pending-reboot" if this is necessary.

Remember that parameter settings can change between major versions, so it's important to review and adjust your parameter groups when performing major version upgrades.
Sources
Aurora PostgreSQL Parameter Group - Compare or Export - Upgrading from 12 to 16 | AWS re:Post
Amazon Aurora PostgreSQL parameters - Amazon Aurora
Viewing parameter values for a DB cluster parameter group in Amazon Aurora - Amazon Aurora