> usually big enough to be stored in a TOAST table
Ah, luckily, in my case, that can’t happen – each row’s message contains one IRC message, so at most 512 bytes. That also automatically ensures we’ll never run into TOAST issues.
Now I understand why you didn't suffer from the slow ranking issue. In my test case, text is longer and triggers the TOAST management code.
Yes, it works, but it is slow because the tsvector is usually big enough to be stored in a TOAST table, and this produces a lot of random access reads.
This is why there is a project of storing additional information in the GIN (term positions) in order for the index to contain all necessary information for the ranking:
https://wiki.postgresql.org/images/2/25/Full-text_search_in_...