@ted_reh if you run

meltano invoke tap-postgres > output.json

can you confirm that your SCHEMA messages include the empty key_properties like you expect? I'm not familiar with this setting but I wonder if https://hub.meltano.com/loaders/target-snowflake#disable_table_cache-setting is relevant? You're right that the target is deciding between merge/copy based on the key properties https://github.com/transferwise/pipelinewise-target-snowflake/blob/aa6ac2e392b6148994f9138241630ba8d684adac/target_snowflake/db_sync.py#L458