presto-rcfile/src/main/java/io/prestosql/rcfile/BufferedOutputStreamSliceOutput.java/BufferedOutputStreamSliceOutput/flushBufferToOutputStream
class BufferedOutputStreamSliceOutput:    private void flushBufferToOutputStream()
    {
        writeToOutputStream(buffer, 0, bufferPosition);
        bufferOffset += bufferPosition;
        bufferPosition = 0;
    }