Large repository - slow svn update

Hi. I have installed svn 1.2.3, and imported a lot of files into it.

Now I am having a slow performance when I do svn update in a working copy.

I am using svn1.2.3 w/apache 2.0.54 (http URLs)

My repository is about 336 Megs, and has 150328 files, including
binaries and text, and has fsfs format.

Why does svn update takes about 1 minute to run, even when it only
updates 4 o 5 files each time ?

I expected it to be much faster, as it is only taking the differences
from my working copy to the HEAD version.