Size of Serialized data is not reducing using flatbuffer

问题

I have written following fbs file

namespace testing;

table polygon {
    x : double;
    y  : double;

}

table layer {
    layer_name : string;
    polygons : [polygon];
}

root_type layer;

My plan is to serialize approx 5 Million coordinates and dump it into one file. Problem is what I see is the number of bytes is increased compared to what I was expecting. I am expecting it should be arounf (5M* 16) bytes. But the size what I am getting is 140000032 bytes

Here is the java code which I am using for dumping serialize data into a file.

FlatBufferBuilder fbb = new FlatBufferBuilder(0);
    String s = "Product1";
    int str = fbb.createString("layer1");
    int size = 1 * 5 * 1000000;
    int[] offset = new int[size];
    int cur = 0;

    for (double i = 0; i < size; i++) {

        fbb.startTable(2);
        polygon.addX(fbb, i);
        polygon.addY(fbb, i);
        offset[cur++] = polygon.endpolygon(fbb);
    }

    int arrayoffset = layer.createPolygonsVector(fbb, offset);
    layer.startlayer(fbb);

    layer.addLayerName(fbb, str);

    layer.addPolygons(fbb, arrayoffset);
    int bla = layer.endlayer(fbb);

    fbb.finish(bla);
    ByteBuffer bf = fbb.dataBuffer().duplicate();

    File myfile = new File("/tmp/test.dat");

    try {
        FileChannel channel = new FileOutputStream(myfile).getChannel();
        channel.write(bf);
        channel.close();

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

Please let me know if I am doing something wrong here

回答1:

change table polygon into struct polygon. table is extensible and has some fixed overhead per element, and also is referred to by the vector over an offset. A struct is not extensible (which seems fine for an xy pair), and has to be serialized inline (see example in the tutorial), and will give you the size you expect.

来源：https://stackoverflow.com/questions/59966568/size-of-serialized-data-is-not-reducing-using-flatbuffer

标签

serialization

flatbuffers