Question on this area. What have you found to be the best way to migrate an existing app to Postgres? We plan to migrate to Postgres, but with every LOC writte

Question on this area. What have you found to be the best way to migrate an existing app to Postgres? We plan to migrate to Postgres, but with every LOC written we're entrenching ourselves into Mysql. We all want Postgres, but at the same time I just can't see the transition happening with each passing day. Thoughts? edit: I should be clear too. I think our goal would be to not require a full rewrite spanning weeks. So an active translation layer, or replication.. or something tricky.. but I just don't foresee us being able to spend a month putting everything on hold so we can migrate.