Hi Tom,
Thanks for taking the time to reply, much appreciated. You get 713KB/
sec, twice as fast as my speed in writing but still half an order of
magnitude slower than the O/S (5MB/sec). The disparity between your
code and mine could easily be explained by fluctuations between runs,
I get a huge amount of variation between runs (up to 30%) which could
be caused by numerous things.
I reported this as a bug in the Android bug tracker and an Android dev
told me he gets 4MB/sec write and 5MB/sec read, and he also suggested
I use arrays to write/read directly to/from streams ... but I still
can't see how he gets that sort of speed.
Thanks for pointing out the problem with the read() idiom, I'm
discarding the result of the call because I'm not using the data and I
just created the file so I know what's in it at that point, but you
are absolutely correct for the general case :-)
On Nov 28, 4:08 pm, "Tom Gibara" <[EMAIL PROTECTED]> wrote:
> Hi Luke,
> Sorry, I did miss your follow-up post. When I got your email I dug out the
> modified code. I'm even more sorry to say that I introduced a dumb bug which
> artificially increased the speed. I accidentally put i += size, instead of i
> += buffer.length. That artificially boosted the speed hugely by outputting a
> small file duh.
>
> Anyway with my modified code (posted below) I get:
>
> 11-28 20:58:09.859: INFO/speedtest(850): speed test a: 1370
> 11-28 20:58:09.889: INFO/speedtest(850): speed test b: 31
>
> which I think is in keeping with your figures (I wouldn't my mental
> arithmetic). I do note however that this idiom in your code:
>
> FileInputStream fis = openFileInput("speedtest");
> fis.read(array);
> fis.close();
>
> is unreliable and only works by chance - in general there is no guarantee
> that any read will fill a buffer unless otherwise noted in the
> documentation.
>
> Hope you didn't waste too much time on my mistake!
>
> Tom.
>
> 2008/11/28 ______ <[EMAIL PROTECTED]>
>
>
>
> > I ran some more extensive tests and got the following:
>
> > WRITING:
> > one byte at a time written to BufferedOutputStream: 155kb/sec
> > whole array written to BufferedOutputStream: 450kb/sec
> > one byte at a time written to FileOutputStream: 8kb/sec
> > whole array written to FileOutputStream: 453kb/sec
>
> > READING:
> > one byte at a time read from BufferedInputStream: 221kb/sec
> > whole array read from BufferedInputStream: 47850kb/sec
> > one byte at a time read from FileInputStream: 9kb/sec
> > whole array read from FileInputStream: 31604kb/sec
>
> > (The reading results are a little artificial as I didn't attempt any
> > sort of buffer flush between tests...)
>
> > This shows that (in the writing case) writing single bytes to a
> > BufferedOutputStream has about a 3x overhead over writing an array to
> > a BufferedOutputStream or FileOutputStream, but writing whole arrays
> > to either buffered or unbuffered streams still does not come close to
> > the numbers you gave. (My arrays are much larger than the default
> > buffer size of 8kb, but that shouldn't make much difference if you
> > were reading actual IO throughput numbers...)
>
> > Anyway the overall result is still an order of magnitude slower than
> > it should be, in the fastest case (using arrays).
>
> > The code is as follows. (The two slowest cases are commented-out.) I
> > get similar numbers using NIO channels. What am I doing differently
> > from you?
>
> > --
>
> > int size = 5 * 1024 * 1024;
> > byte[] array = new byte[size];
>
> > long startTime = System.currentTimeMillis();
> > BufferedOutputStream bos = new
> > BufferedOutputStream(openFileOutput
> > ("speedtest", MODE_PRIVATE));
> > for (int i = 0; i < size; i++)
> > bos.write((byte) 0);
> > bos.close();
> > Log.i("speedtest", "one byte at a time written to
> > BufferedOutputStream: " + ((size / 1024.0) / ((System.currentTimeMillis
> > () - startTime) / 1000.0)) + "kb/sec");
>
> > // startTime = System.currentTimeMillis();
> > // FileOutputStream fos = openFileOutput("speedtest",
> > MODE_PRIVATE);
> > // for (int i = 0; i < size; i++)
> > // fos.write((byte) 0);
> > // fos.close();
> > // Log.i("speedtest", "one byte at a time written to
> > FileOutputStream: " + ((size / 1024.0) / ((System.currentTimeMillis()
> > - startTime) / 1000.0)) + "kb/sec");
>
> > startTime = System.currentTimeMillis();
> > bos = new
> > BufferedOutputStream(openFileOutput("speedtest",
> > MODE_PRIVATE));
> > bos.write(array);
> > bos.close();
> > Log.i("speedtest", "whole array written to
> > BufferedOutputStream: "
> > + ((size / 1024.0) / ((System.currentTimeMillis() - startTime) /
> > 1000.0)) + "kb/sec");
>
> > startTime = System.currentTimeMillis();
> > FileOutputStream fos = openFileOutput("speedtest",
> > MODE_PRIVATE);
> > fos.write(array);
> > fos.close();
> > Log.i("speedtest", "whole array written to
> > FileOutputStream: " +
> > ((size / 1024.0) / ((System.currentTimeMillis() - startTime) /
> > 1000.0)) + "kb/sec");
>
> > startTime = System.currentTimeMillis();
> > BufferedInputStream bis = new
> > BufferedInputStream(openFileInput
> > ("speedtest"));
> > for (int i = 0; i < size; i++)
> > bis.read();
> > bis.close();
> > Log.i("speedtest", "one byte at a time read from
> > BufferedInputStream: " + ((size / 1024.0) / ((System.currentTimeMillis
> > () - startTime) / 1000.0)) + "kb/sec");
>
> > // startTime = System.currentTimeMillis();
> > // FileInputStream fis = openFileInput("speedtest");
> > // for (int i = 0; i < size; i++)
> > // fis.read();
> > // fis.close();
> > // Log.i("speedtest", "one byte at a time read from
> > FileInputStream:
> > " + ((size / 1024.0) / ((System.currentTimeMillis() - startTime) /
> > 1000.0)) + "kb/sec");
>
> > startTime = System.currentTimeMillis();
> > bis = new
> > BufferedInputStream(openFileInput("speedtest"));
> > bis.read(array);
> > bis.close();
> > Log.i("speedtest", "array read from
> > BufferedInputStream: " +
> > ((size / 1024.0) / ((System.currentTimeMillis() - startTime) /
> > 1000.0)) + "kb/sec");
>
> > startTime = System.currentTimeMillis();
> > FileInputStream fis = openFileInput("speedtest");
> > fis.read(array);
> > fis.close();
> > Log.i("speedtest", "array read from FileInputStream:
> > " + ((size /
> > 1024.0) / ((System.currentTimeMillis() - startTime) / 1000.0)) + "kb/
> > sec");
>
> > deleteFile("speedtest");
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