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.
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select 
    table_schema
  , table_name
  , data_type
from information_schema.columns
where table_schema = 'public'
  and table_name= 'pgbench_accounts'
order by ordinal_position;
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and use something like that to md5 (or another checksum), either as a whole or on a row-by-row basis, or both.