Why is IntelliJ IDEA hanging on "Indexing"?

I've finally figured it out. The solution was... Rather odd. TL;DR: Run it under strace. Read on for a more detailed explanation.

I came upon it when I decided to run IntelliJ under strace to see what files it was opening to determine whether or not it was a filesystem bottleneck.

This gave me some very strange results: strace was spewing out a near-constant stream of segfaults. Not only that, but IntelliJ was running just fine, not taking forever to index.

After consulting with a friend, I learned that on Arch Linux, systemd logs a dump of a process's memory every time a segfault occurs, except when a debugger is attached. strace is considered a debugger. Arch was thrashing my disks when it kept logging memory dumps due to all the segfaults, hence why the indexing was taking so long, because it was fighting for disk I/O.

My solution for now is to simply run IntelliJ under strace. I will, however, be looking into the issue further, as I don't think java should be segfaulting that much.

edit Intellij[VERSION]/bin/idea.properties, set idea.max.intellisense.filesize=50

update: Intellij will skip index files that size larger than 50kb.try this if you have many libraries or many large files(too many characters one line or too many lines)

I had this issue as well with version 2016.2 on Mac OS X. I had to do a force quit to end the application, then I deleted the .idea folder. The next time I launched IntelliJ everything worked fine, it had no problem indexing the project.

Try Invalidating the cache and restarting IntelliJ.

In the File menu, select Invalidate Caches / Restart... and then click the Invalidate and Restart button.