Change checkpoint_data and restore_connection_on_error to subtransaction checkpoint_data and restore_connection_on_error used to commit() and rollback() the db connection. This causes additional I/O and load. Changed them to use 'SAVEPOINT name' and 'ROLLBACK TO name' to get a faster method for handling errors within a tranaction. One thing to note is that postgresql (unlike SQL std) doesn't overwrite an older savepoint with he same name. It keeps all savepoints but only rolls back to the newest one with a given name. This could be a resource issue. I left a commented out release statement in case somebody runs into an issue due to too many savepoints. I expect it to slow down the import but....

try:
    from html import escape as html_escape_  # python 3

    def html_escape(str, quote=False):
        # html_escape under python 3 sets quote to true by default
        # make it python 2 compatible
        return html_escape_(str, quote=quote)
except ImportError:
    # python 2 fallback
    from cgi import escape as html_escape  # noqa: F401