Optimal buffer size for output stream

Question

I'm writing a method to save an input stream to an output stream. What's the optimal size for the buffer? Here's my method:

/**
* Saves the given InputStream to a file at the destination. Does not check whether the destination exists.
*
* @param inputStream
* @param destination
* @throws FileNotFoundException
* @throws IOException
*/
public static void saveInputStream(InputStream inputStream, File outputFile) throws FileNotFoundException, IOException {
 try (OutputStream out = new FileOutputStream(outputFile)) {
 byte[] buffer = new byte[2097152]; //This is set to two MB. But I have no idea whether this is optimal
 int length;
 while ((length = inputStream.read(buffer)) > 0) {
 out.write(buffer, 0, length);
 }
 inputStream.close();
 }
}

Answer 1

It depends on a lot of factors, there's no universally "optimal" size. 512kB is probably good enough.

If you want, you can always benchmark it for various buffer sizes: this will let you know what the best option is for your computer and OS.

• kentcdodds: Just asked a question about getting the block size. Could be useful. But I think you're right :)
• Quentin Pradet: You still should benchmark it. You'll be surprised by the results!