presto-spi/src/main/java/io/prestosql/spi/block/RowBlock.java/RowBlock/isLoaded
class RowBlock:    @Override
    public boolean isLoaded()
    {
        for (Block fieldBlock : fieldBlocks) {
            if (!fieldBlock.isLoaded()) {
                return false;
            }
        }
        return true;
    }