def updateTimezones(db):
    """
    Update UTC offses in 'timezones' with values in 'pg_timezone_names'

    The UTC offsets in 'pg_timezone_names' are DST adjusted (for the timezones
    we care about) so we need to copy the values regularly to keep the cached
    values in 'timezones' up-to-date.
    """
    import base
    if base.configuration()['database.driver'] == 'postgresql':
        with db.updating_cursor('timezones') as cursor:
            cursor.execute(
                """UPDATE timezones
                                 SET utc_offset=pg_timezone_names.utc_offset
                                FROM pg_timezone_names
                               WHERE pg_timezone_names.name=timezones.name"""
                )
