doOpenIfChanged
Implement this method to support .openIfChanged. If this reader does not support reopen, return null, so client code is happy. This should be consistent with .isCurrent (should always return true) if reopen is not supported.
Return
null if there are no changes; else, a new DirectoryReader instance.
Throws
if there is a low-level IO error
Implement this method to support .openIfChanged. If this reader does not support reopen from a specific IndexCommit, throw [ ].
Return
null if there are no changes; else, a new DirectoryReader instance.
Throws
if there is a low-level IO error
Implement this method to support .openIfChanged. If this reader does not support reopen from IndexWriter, throw [ ].
Return
null if there are no changes; else, a new DirectoryReader instance.
Throws
if there is a low-level IO error