private int getBlobPdxTypeId(byte[] blob) {
    ByteBuffer bb = ByteBuffer.wrap(blob);
    // skip byte for PDX dscode and integer for pdx length
    return bb.getInt(DataSize.BYTE_SIZE + DataSize.INTEGER_SIZE);
  }
Make sure that if a class adds a field that pdx serialization will preserve the extra field.
geode-core/src/integrationTest/java/org/apache/geode/pdx/PdxSerializableJUnitTest.java