Symptoms

Confluence Space Usage Statistic page is not shown. 

The following appears in the atlassian-confluence.log:

2013-11-06 05:17:33,762 ERROR [main] [atlassian.plugin.manager.DefaultPluginManager] enableConfiguredPluginModule There was an error loading the descriptor 'Usage Index Manager' of plugin 'com.atlassian.confluence.ext.usage'. Disabling.
com.atlassian.bonnie.LuceneException: Failed to create searcher for directory: org.apache.lucene.store.SimpleFSDirectory@<confluence-home>/index/plugin/usage lockFactory=org.apache.lucene.store.SimpleFSLockFactory@4f882760

Diagnosis

Even though the user that run Confluence has enough read/write permission to <confluence-home>/index/plugin/usage directory, accessing Space Usage Statistic screen still throws the error trace above. However, migrating the instance to a new Home Directory solves the issue.

Cause

The index directory is corrupted during migration/upgrade or failure when restarting/shutting down Confluence instance.

Resolution

• Clear plugin cache

• If it doesn't work, try to rebuild content indices from scratch

• Otherwise, remove all the content of <confluence-home>/index/plugin/usage/ directory