title: High idle CPU usage for MongoDB on Ubuntu guest VM
body: <p>I'm running an Ubuntu 12.04 server instance on VirtualBox on a OS X 10.7 host (MacBook Air 13"). The instance is configured with 512mb ram. The disk image is set to 8GB (dynamically allocated if that makes any difference) and is using 2.6GB.</p>
  
  <p>I've just installed MongoDB from the 10gen repo as described here: <a href="http://docs.mongodb.org/manual/tutorial/install-mongodb-on-debian-or-ubuntu-linux/" rel="nofollow">http://docs.mongodb.org/manual/tutorial/install-mongodb-on-debian-or-ubuntu-linux/</a></p>
  
  <p>I haven't changed any of the default settings as yet.</p>
  
  <p>The mongod process is now running at 15-20% cpu constantly, before I've connected anything to it. I wouldn't normally have checked but it's now causing the fans to stay on whenever the VM is running.</p>
  
  <p>Restarting mongodb makes no difference. Restarting the VM makes no difference.</p>
  
  <p>The log is as follows:</p>
  
  <pre><code>Thu Jun 21 16:52:14 [initandlisten] MongoDB starting : pid=1737 port=27017 dbpath=/var/lib/mongodb 64-bit host=devbox
  Thu Jun 21 16:52:14 [initandlisten] db version v2.0.6, pdfile version 4.5
  Thu Jun 21 16:52:14 [initandlisten] git version: e1c0cbc25863f6356aa4e31375add7bb49fb05bc
  Thu Jun 21 16:52:14 [initandlisten] build info: Linux ip-10-110-9-236 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20 17:48:28 EST 2009 x86_64 BOOST_LIB_VERSION=1_41
  Thu Jun 21 16:52:14 [initandlisten] options: { config: "/etc/mongodb.conf", dbpath: "/var/lib/mongodb", logappend: "true", logpath: "/var/log/mongodb/mongodb.log" }
  Thu Jun 21 16:52:14 [initandlisten] journal dir=/var/lib/mongodb/journal
  Thu Jun 21 16:52:14 [initandlisten] recover : no journal files present, no recovery needed
  Thu Jun 21 16:52:14 [initandlisten] waiting for connections on port 27017
  Thu Jun 21 16:52:14 [websvr] admin web console waiting for connections on port 28017
  </code></pre>
  
  <p>I'm assuming 15-20% cpu usage at idle isn't normal, so I'd like to know if anyone has any suggestions on what to try to fix it?</p>
  
  <p><em>edit</em>
  I've now converted the disk image to a fixed size VDI and it's made no difference, still at 15-20% CPU usage on the guest.</p>