How do you decide what byte[] size to use for InputStream.read()?

Question

When reading from InputStreams, how do you decide what size to use for the byte[]?

int nRead; byte[] data = new byte[16384]; // <-- this number is the one I'm wondering about  while ((nRead = is.read(data, 0, data.length)) != -1) {   ...do something.. } 

When do you use a small one vs a large one? What are the differences? Does the number want to be in increments of 1024? Does it make a difference if it is an InputStream from the network vs the disk?

Thanks much, I can't seem to find a clear answer elsewhere.

Answer 1

Most people use powers of 2 for the size. If the buffer is at least 512 bytes, it doesn't make much difference ( < 20% )

For network the optimal size can be 2 KB to 8 KB (The underlying packet size is typically up to ~1.5 KB) For disk access, the fastest size can be 8K to 64 KB. If you use 8K or 16K you won't have a problem.

Note for network downloads, you are likely to find you usually don't use the whole buffer. Wasting a few KB doesn't matter much for 99% of use cases.

Answer 2

In that situation, I always use a reasonable power of 2, somewhere in the range of 2K to 16K. In general, different InputStreams will have different optimal values, but there is no easy way to determine the value.

In order to determine the optimal value, you'd need to understand more about the exact type of InputStream you are dealing with, as well as things like the specifications of the hardware that are servicing the InputStream.

Worrying about this is probably a case of premature optimization.