Programming

Thanks Jim. Well i have to do evaluate buffer size for repeated random file access. im sorry but being a novice.. i dint get what your shell script does here?

I am trying to randomly read a file from a simple C program, how can i clear cache from there before each read? any ideas?

if you force OS to read big enough file[s] before running your program, the cache would become irrelevant. Under *nix you can say
wc -c some-big-files > /dev/null
so OS will read those files and pages from your file that your program reads will hopefully be eliminated from cache

The post from jim mcnamara is a good demo showing the effect of buffer sizes on the time taken to read a large file. From the table it looks like 4kb is the optimal size for the buffer most likely because that is the system pagesize.

@jim:
The math doesn't add up for the last three rows of that table that is User + System != Elapsed...
The skewness introduced by caching can be offset to some extent by starting the program with the highest buffer size and reducing it at every step.