What exactly returns IndexReader.numDeletedDocs()

[Michael Wechner]

Hi

I am using Lucen 9.4.2 vector search and everything seems to work fine, 
except that when I delete some documents from the index, then the method

https://lucene.apache.org/core/9_0_0/core/org/apache/lucene/index/IndexReader.html#numDeletedDocs()

always returns 0, whereas I would have expected that it would return the 
number of documents which I deleted from the index.

IndexReader.numDocs() returns the correct number though.

I guess I misunderstand the javadoc and in particular the note "*NOTE*: 
This operation may run in O(maxDoc)."

Does somebody explain in more detail what this method is doing?

Thanks

Michael