Make Bytes.toStringBinary faster

Bytes.toStringBinary is quite expensive due to its use of String.format. It seems to me that String.format is overkill for the purpose and I could actually make the function up to 45-times faster by replacing the part with a simpler hand-crafted code.

This is probably a non-issue for HBase server as the function is not used in performance-sensitive contexts but I figured it wouldn't hurt to make it faster as it's widely used in builtin tools - Shell, HFilePrettyPrinter with -p option, etc. - and it can be used in clients.

Background:

We have an HBase monitoring tool that periodically collects the information of the regions and it calls Bytes.toStringBinary during the process to make some information suitable for display. Profiling revealed that a large portion of the processing time was spent in String.format.

Micro-benchmark:

byte[] bytes = new byte[256];
for (int i = 0; i < bytes.length; ++i) {
  // Mixture of printable and non-printable characters.
  // Maximal performance gain (45x) is observed when the array is solely
  // composed of non-printable characters.
  bytes[i] = (byte) i;
}
long started = System.nanoTime();
for (int i = 0; i < 1000000; ++i) {
  Bytes.toStringBinary(bytes);
}
System.out.println(TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - started));

• Without the patch: 134176 ms
• With the patch: 3890 ms

I made sure that the new version returns the same value as before and simplified the check for non-printable characters.