You can always build a small search webservice that you open source and that your proprietary software calls out too, removing the need to open source everything.

Linux is GPL too, didn't hinder companies making trillions on top of it.

A lot more than a decade. I've been using it for 15 years at it was a very mature project even then. Repo history goes back to 1999 and according to the history page the project's roots go back to the 80s. A bit like Postgres in this respect.

https://xapian.org/history https://sigir.org/files/forum/S2000/MUSCAT_note.pdf

For what kind of use do you think GPLv2 would be a blocker?

I used it commercially, at a very big international company. All users had access to its unmodified source code and templates. There was no trouble at all.

In fact, AIUI it's roots go back about 3 decades. The "about" page has a nice historical overview.-

The project at one point started tracking files for potential rewrite to rid itself of GPL history. I used it many years ago and I quite enjoyed it (pre elastic search times) but unfortunately the license situation didn’t help the project to become popular.

that's true, wonder if there is alternative that is not gpl