Precompiled headers using boost libs takes very long to compile
<p>I'm creating a software that relies on a lot of boost libs and, as compilation became slower and slower (minutes), I've packed all the libs used over and over in a precompiled header (say 20-ish boost libs and 20 std libs), hoping that it would solve the issue.</p>

<p>Today, I realized that a vanilla hello-world.cpp (that does not even includes the damn precompiled header) takes 15s to build when i compile with the precompiled header. The precompiled header is 300MB or so.</p>

<p>Hence, the questions are:</p>

<p>-is that kind of slowdown expected, for a precompiled header this size? 
(I secretely hope that I made some kind of monstruous mistake and I'd be very happy if one of you could tell me that he routinely works with a 2GB precompiled header and things are smooth)</p>

<p>-if this kind of slowdown is expected, then I'm not convinced at all at the usefullness of a precompiled header. Am I missing something?</p>

<p>compiler:</p>

<pre><code>gcc version 4.4.5 (Debian 4.4.5-8)
</code></pre>

<p>commandline: </p>

<pre><code>g++ -include common-header.hpp -Winvalid-pch -c vanilla-hello-world.cpp
</code></pre>
