Re: Why is network reading slow?

Peter Olcott wrote:


True, if the DOS copy command is fast,then I believe the
code you are using is not optimal. The DOS Copy is using
the same CreateFile() API which fopen() also finally uses
in the RTL. So you should be able to match the same
performance of the DOS Copy command.

Have you tried using setvbuf to set a buffer cache?

Here is a small test code that opens a 50 meg file:

// File: V:\wc7beta\testbufsize.cpp
// Compile with: cl testbufsize.cpp

#include <stdio.h>
#include <windows.h>

void main(char argc, char *argv[])
{
   char _cache[1024*16] = {0}; // 16K cache
   BYTE buf[1024*1] = {0}; // 1K buffer

   FILE *fv = fopen("largefile.dat","rb");
   if (fv) {
       int res = setvbuf(fv, _cache, _IOFBF,
sizeof(_cache));
       DWORD nTotal = 0;
       DWORD nDisks = 0;
       DWORD nLoops = 0;
       DWORD nStart = GetTickCount();
       while (!feof(fv)) {
            nLoops++;
            memset(&buf,sizeof(buf),0);
            int nRead = fread(buf,1,sizeof(buf),fv);
            nTotal +=nRead;
            if (nRead > 0 && !fv->_cnt) nDisks++;
       }
       fclose(fv);
       printf("Time: %d | Size: %d | Reads: %d | Disks:
%d\n",
               GetTickCount()-nStart,
               nTotal,
               nLoops,
               nDisks);
    }
}

What this basically shows is the number of disk hits it
makes
by checking the fv->_cnt value. It shows that as long as
the cache size is larger than the read buffer size, you
get the same number of disk hits. I also spit out the
milliseconds. Subsequent runs, of course, is faster since
the OS API CreateFile() is used by the RTL in buffer mode.

Also do you know what protocol you have Samba using?

--
HLS