In my case I found out that Intellij is actually trying to index a 50GB directory with logs that was under the project's root. Make sure that if you have such a directory, it is marked as "Excluded" in the IDE.
You can see which file the IDE is indexing currently in the Indexing Status window (access by clicking on the indexing message in the toolbar). You may need to enlarge this window to see the full path of the file currently being indexed.
