Re[jcifs] ading files using SmbFileInputStream

[Michael B Allen]

On Mon, Jun 15, 2009 at 11:01 AM, aviv<avivf at mailinator.com> wrote:
>
> Hello, I've been using jcifs for quite (version 1.3.9) a while and must say
> I'm impressed. However, I've noticed that transferring files from my server
> to my local machine takes a very long time. Here is the code I use to
> transfer the file:
>
> InputStream in = new SmbFileInputStream(remoteFile);
> OutputStream out = new FileOutputStream(localFile);
> byte[] buffer = new byte[16904];
> int read = 0;
> while ((read = in.read(buffer) > 0)
>    out.write(buffer, 0, read);
> in.close();
> out.close();
>
> Now, this can take about 40 seconds for a 1.2MB file. When copying the file
> using Windows Explorer, however, it only takes about 10 seconds. I decided
> to try and find out what the difference was. Using Wireshark I noticed that
> in the ReadAndXRequests issued from Windows Explorer each read was 61440
> bytes of length, while those issued from jcifs were 4356 bytes consistently.
> Upon further investigation, I saw that in SmbFileInputStream the requests
> are sent with a maximal length of transport.server.maxBufferSize, which
> apparently in my case is 4356. I've tried changing the
> jcifs.smb.client.rcv_buf_size but since the request sizes are bound to
> server.maxBufferSize, it didn't help.
>
> To sum it up, why would the maxBufferSize be different for jcifs as opposed
> to Windows Explorer? Is it possible to take maxBufferSize as a
> recommendation and send requests with larger sizes?

The most important factor in transfer performance is to put as much
data into each packet as possible.  So larger buffer sizes do not
necessarily improve transfer speed. In fact they can decrease
performance if for example every other packet contains only a small
fragment of the stream.

In general JCIFS is pretty fast but even 10 seconds to transfer a 1.2
MB file is pretty slow so I have to wonder if your network just has a
really high latency and that has a significant impact because JCIFS is
exchanging more packets in the transfer.

There are multiple buffer settings you can play with. You should be
able to match the buffer settings used by Windows Explorer in which
case you should get similar performance. You have to analyze WireShark
and fiddle with writeSize, snd_buf_size and rcv_buf_size until you get
similar results to the Windows Explorer capture.

But in general, unless performance in a particular environment is
really critical, you shouldn't mess with these settings because you'll
make it fast in one case and slow in all the other cases.

Mike

-- 
Michael B Allen
Java Active Directory Integration
http://www.ioplex.com/