You are seeing
ERROR: must be owner of extension plpgsql or similar when you attempt to run
When Rails generates
structure.sql, it includes commands to enable the database extensions it wants to use. Unfortunately, these are blocked by
heroku-postgresql. One way around this is to use
config.active_record.schema_format = :ruby, which means your app would generate a
schema.rb instead of a
schema.rbis compatible with
heroku-postgresql because it doesn't enable extensions.
If you need to use
structure.sql you can remove
COMMENT ON EXTENSION plpgsql IS 'PL/pgSQL procedural language'; which should also resolve this issue.