[CentOS] fast processing and buffering

[Kwan Lowe]

On Wed, Mar 2, 2011 at 10:59 AM, Michael D. Berger
<m_d_berger_1900 at yahoo.com> wrote:
> I have a C++ program that opens, gets a little data from, and closes
> about 5000 files.  Now if I run the program when I first boot up,
> the running time is from about 10 seconds to a minute.  Subsequently,
> the program runs in well inter one second.  Buffering -- right?
>
> So I changed a parameter, so the program gets a different (albeit
> similar) 5000 files from a different directory.  Running time on
> the first try:  well under one second.
>
> How about that?
>
> [~]$ uname -a
> Linux xxxxx 2.6.18-194.32.1.el5 #1 SMP Wed Jan 5 17:53:09 EST 2011 i686
> i686 i386 GNU/Linux

Buffering, certainly.. but maybe on several layers.   The physical
disk may have a read ahead cache. The OS may also buffer.

You may also be pulling in libraries on the initial run which stay
resident for awhile..