Index stops functioning because org.apache.lucene.store.AlreadyClosedException is not handled correctly

Summary

Sometimes any operations on the index, for example searching, will cease functioning. In the logs there will be an error like:

com.atlassian.jira.issue.index.SearchUnavailableException: com.atlassian.util.concurrent.LazyReference$InitializationException: org.apache.lucene.store.AlreadyClosedException: this IndexReader is closed

Cause

The org.apache.lucene.store.AlreadyClosedException exception is not being handled correctly.

Workaround

One of the following will get it working again:

1. Restart Confluence
2. Rebuild Indexes from scratch