Issue Summary

Confluence Lucene connection uses NIOFSDirectory implementation rather than MMapDirectory in Java 11

Steps to Reproduce

1. Install any Confluence version above 7.X that has support for Java 11
2. The underlying Lucene uses NIOFSDirectory implementation rather than MMapDirectory which is more efficient

Expected Results

Confluence should use MMapDirectory with Java 11 as it was with Java 8

Actual Results

Confluence uses NIOFS implementation . This can result in multiple outcomes

1. At scale, this method can be notably less performant for index lookups and searches
2. Conditionally this results in situations where customers are presented with below error that requires a restart of the instance

   aused by: java.io.IOException: null: NIOFSIndexInput(_f2fd_Lucene41_0.tim in path="/var/atlassian/application-data/confluence/index/_f2fd.cfs" slice=2604086:9597840)
   	at org.apache.lucene.store.NIOFSDirectory$NIOFSIndexInput.readInternal(NIOFSDirectory.java:191)
   	... 143 more
   Caused by: java.nio.channels.ClosedByInterruptException
   

   This is a known behaviour for NIOFS class https://lucene.apache.org/core/3_5_0/api/all/org/apache/lucene/store/NIOFSDirectory.html

   • NOTE: Accessing this class either directly or indirectly from a thread while it's interrupted can close the underlying file descriptor immediately if at the same time the thread is blocked on IO. The file descriptor will remain closed and subsequent access to NIOFSDirectory will throw a ClosedChannelException. If your application uses either Thread.interrupt() or Future.cancel(boolean) you should use SimpleFSDirectory in favor of NIOFSDirectory.

Workaround

Downgrade to Java 8