We are continuing to work on improving the performance of the Maven repository. Last week Sonatype suggested that we remove the custom-metadata-plugin due to a possible memory leak. We also increased the amount of memory available to Nexus from 512 MB to 1024 MB. This was done Monday (Apr 26) evening and the server was restarted. This seems to have improved the memory issues.
We also had a problem starting last Thursday (Apr 29) where certain maven metadata files could not be downloaded. The server logs contained an error message about too many files being open on the server. Gradually more files became locked until the whole system became unresponsive. After restarting Nexus, this problem disappeared. The operating system open files limit on the server has also been increased to avoid this problem in the future.
This week Sonatype made a configuration change to our authentication configuration (moving the internal Nexus realm before the http realm) which should improve the performance of the security system, and reduced some of the errors/warning we were seeing in the logs. We have also noticed some timeouts (http://community.jboss.org/thread/151522) when deploying snapshots to the server, but we have not yet determined the cause of this.
In the near future we're also planning to change the configuration of our QA environment (hudson) which should reduce the load on our main repository server. We're also planning to upgrade Nexus to version 1.6.0 which includes many bug fixes.