Symptoms

When you try to enable the usage stat plugin into UPM you will get an error similar as the below one in the atlassian-confluence.log:

There was an error loading the descriptor 'Usage Index Manager' of plugin 'com.atlassian.confluence.ext.usage'. Disabling.
 -- referer: http://mymachine.com:8094/confluence/plugins/servlet/upm/manage/system | url: /confluence/rest/plugins/1.0/com.atlassian.confluence.ext.usage-key | userName: username
com.atlassian.bonnie.LuceneException: Failed to create searcher for directory: org.apache.lucene.store.SimpleFSDirectory@/home/confluenceconfluence-home/index/plugin/usage lockFactory=org.apache.lucene.store.SimpleFSLockFactory@1f3e82c
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Caused by: java.io.FileNotFoundException: /home/confluence/confluence-home/index/plugin/usage/segments_1ix1m (No such file or directory)

Cause

During the upgrade process some files inside <confluence-home>/index/plugin and/or <confluence-home>/index/edge were corrupted resulting in search plugins not enabling.

Resolution

Following the steps in How to Rebuild the Content Indexes From Scratch on Confluence Server, do not replace the backups made in step two or three depending on the plugin you are having problems with enabling. After the rebuild you will be able to enable those plugins, however your Usage and/or Edge data will be lost. Below goes the detailed steps:

1. Shut down your Confluence server.

2. Backup <confluence-home>/index/plugin - this is where the Usage Tracking Plugin stores the usage statistics.

3. Backup <confluence-home>/index/edge - this is where the index of Likes and Popular Content are stored.

4. Remove the <confluence-home>/index directory.
5. Create <confluence-home>/index,
6. Check which plugin you are unable to enable, if its Usage stats only, copy the backup made in step 3 into the newly created index folder, if it's edge plugin only do this action to the backup made into step 2 and lastly if are both DO NOT copy back any of those.
7. Restart Confluence.