optimal buffer size for reading file in C [closed]

Question

I have to read large files in C using read function. I was just wondering if it makes any difference what buffer size we keep in terms of performance. The file sizes may reach till tens of GB.

Answer 1

Short version.
It depends. On x86 buffer size of 4096 bytes is a good start (one page size and also Advanced Format block size).

Longer version.
In UNIX it depends on kernel, libc, filesystem, hardware, etc. Not only on versions and compilation options but also on run-time tunables(e.g read ahead setup).

DIY.
Test it! See Advanced Programing in UNIX Environment Chapter 3.9 "I/O Efficiency" for straightforward way of determining the best read-write buffer size for one particular system.