presto-record-decoder/src/main/java/io/prestosql/decoder/avro/AvroRowDecoderFactory.java/AvroRowDecoderFactory/create
class AvroRowDecoderFactory:    @Override
    public RowDecoder create(Map<String, String> decoderParams, Set<DecoderColumnHandle> columns)
    {
        String dataSchema = requireNonNull(decoderParams.get("dataSchema"), "dataSchema cannot be null");
        Schema parsedSchema = (new Schema.Parser()).parse(dataSchema);
        return new AvroRowDecoder(new GenericDatumReader<>(parsedSchema), columns);
    }