Just for the sake of logging things done, this is how pruning the PROD db was done - it is conceptually the same as what was done for STG, so I'm not adding the comments.

$ pg_dump -Fc resultsdb > resultsdb.dump
$ createdb -T template0 resultsdb_archive
$ pg_restore -d resultsdb_archive resultsdb.dump
$ psql resultsdb_archive
=# select id, job_id from result where submit_time<'2017-01-10' order by submit_time desc limit 1;
    id    | job_id 
----------+--------
 11604818 | 387701

=# select id, job_id from result where job_id > 387701 order by id limit 1;
    id    | job_id
----------+--------
 11604819 | 387702

=# delete from result_data where result_id >= 11604819;
=# delete from result where id >= 11604819;
=# delete from job where id >= 387702;

$ psql resultsdb

=# delete from result_data where result_id < 11604819;
=# delete from result where id < 11604819;
=# delete from job where id < 387702;