presto-hive/src/main/java/io/prestosql/plugin/hive/HiveWriterFactory.java/HiveWriterFactory/computeBucketedFileName
class HiveWriterFactory:    public static String computeBucketedFileName(String queryId, int bucket)
    {
        String paddedBucket = Strings.padStart(Integer.toString(bucket), BUCKET_NUMBER_PADDING, '0');
        return format("0%s_0_%s", paddedBucket, queryId);
    }