fadvise is a command used to give file advisory information to the operating system.
Its "don't need" option (fadvise --dontneed) is particularly useful to cause the files' pages (blocks) to be evicted from the buffer-cache.

Here is some sample output:

$ fadvise --verbose --dontneed foo.rrd
page size: 4096
foo.rrd: no incore pages.

And the usage information:

Usage:
    fadvise [options] file [...]

     Options:
      -help - brief help message
      -man - full documentation
      -sequential
      -random
      -willneed
      -dontneed
      -noreuse
      -normal (default)
      -offset=n
      -length=n
      -verbose
      -noverbose

The fadvise command was introduced in the paper, "Application Buffer-Cache Management for Performance: Running the World's Largest MRTG", that appears in the proceedings of the LISA 2007 conference in Dallas, November, 2007.
It is available online here:
http://www.usenix.org/events/lisa07/tech/plonka.html

You may also be interested in the related fincore command.

Dave Plonka, May 21 2007