I don't really see the problem. That oracle get_dll() just gets you the metadata. Every database can give you metadata.
An easy way in postgres is to use the views in schema information_schema.
To see a list in psql:
\dv information_schema.
select
table_schema
, table_name
, data_type
from information_schema.columns
where table_schema = 'public'
and table_name= 'pgbench_accounts'
order by ordinal_position;
and use something like that to md5 (or another checksum), either as a whole or on a row-by-row basis, or both.