presto-spi/src/main/java/io/prestosql/spi/block/SingleMapBlockWriter.java/SingleMapBlockWriter/SingleMapBlockWriter
class SingleMapBlockWriter:    SingleMapBlockWriter(int start, BlockBuilder keyBlockBuilder, BlockBuilder valueBlockBuilder)
    {
        this.offset = start;
        this.keyBlockBuilder = keyBlockBuilder;
        this.valueBlockBuilder = valueBlockBuilder;
        this.initialBlockBuilderSize = keyBlockBuilder.getSizeInBytes() + valueBlockBuilder.getSizeInBytes();
    }