Any major performance change with I/O from JDK 6 that one should be aware of?

[Alan Bateman]

On 13/05/2012 17:35, Fabrizio Giudici wrote:
> I've just succesfully ported to OpenJDK 7 a small desktop application 
> that was previously running with Apple's JDK 6. The application 
> computes at the maximum speed possible the MD5 fingerprints of files 
> in a directory. The performance with Apple JDK 6 is about 95-100 
> MB/sec (which is reasonably limited by my disk native I/O speed). The 
> same application with OpenJDK 7 runs under 7 MB/sec.
>
> Loading is done by means of MappedByteBuffer:
>
>             final @Cleanup RandomAccessFile randomAccessFile = new 
> RandomAccessFile(file, "r");
>             final MappedByteBuffer byteBuffer = 
> randomAccessFile.getChannel().map(READ_ONLY, 0, file.length());
>             byteBuffer.load();
>             randomAccessFile.close();
>
> From preliminary measurement, the bottleneck is with I/O. In fact, 
> with JDK 6 the application takes most of the CPU (MD5 is computed in 
> parallel to I/O), while with OpenJDK 7 the CPU is much lower.
>
> Of course I've tested the same application bits side by side with 
> Apple JDK 6 and OpenJDK 7 on the same set of files.
>
The above is essentially open + mmap + madvise and there hasn't been 
anything of significant between 6 and 7 that comes to mind, unless of 
course Apple's jdk6 specifies different advice that improves this case. 
The only thing that comes to mind is the security provider, maybe there 
is a different MD5 implementation that is being used.

-Alan.