Hello, Sergey!

I have addressed your comments:
* skip TID scan in case of empty STIR index
* fix for critical section
* formatting
* index_create signature

Rebased, patch structure and comments available here [0]. Quick
introduction poster - here [1].

Best regards,
Mikhail.

[0]: https://www.postgresql.org/message-id/flat/CADzfLwVOcZ9mg8gOG%2BKXWurt%3DMHRcqNv3XSECYoXyM3ENrxyfQ%40mail.gmail.com#52c97e004b8f628473124c05e3bf2da1
[1]: https://www.postgresql.org/message-id/attachment/176651/STIR-poster.pdf