Getting number of disk accesses from BufferedStream

Question

I'm reading a binary file using BinaryReader. I want to count the number of disk accesses when buffering input with BufferedStream. Unfortunately this class is sealed, so I can't override method to count it manually.

Is there any way of doing it using standard library? Or must I write my own buffering BinaryReader to achieve this?

Answer 1

You could just calculate it from the buffer size you specified in the BufferedStream(Stream, int) constructor. The default is 4096 bytes. Assuming you don't Seek(), the number of file accesses is (filesize + bufsize - 1) / bufsize.

A total overkill approach is to keep in mind that you can chain streams. Create your own Stream derived class and just count the number of calls to the Read() method that need to supply data from the underlying stream. Pass an instance of that class to the BufferedStream constructor.

Neither approach lets you find out how often the operating system hits the disk driver and physically transfers data from the disk. The file system cache sits in between and the actual number greatly depends on how the file data is mapped across the disk cylinders and sectors. You'd get info about that from a performance counter. There's little point in actually using it, the numbers you get will very poorly reproduce on another machine.