Stanislav Kozlovski <Stanislav_Kozlovski@xxxxxxxxxxx> writes: > I was aware of the limitations of FTS<https://www.postgresql.org/docs/17/textsearch-limitations.html> and tried to ensure I didn't hit any - but what I missed was that the maximum allowed lexeme position was 16383 and everything above silently gets set to 16383. I was searching for a phrase (two words) at the end of the book and couldn't find it. After debugging I realized that my phrase's lexemes were being set to 16383, which was inaccurate. > ... > The problem I had is that it breaks FOLLOWED BY queries, essentially stopping you from being able to match on phrases (more than one word) on large text. Yeah. FOLLOWED BY didn't exist when the tsvector storage representation was designed, so the possible inaccuracy of the lexeme positions wasn't such a big deal. > Why is this still the case? Because nobody's done the significant amount of work needed to make it better. I think an acceptable patch would have to support both the current tsvector representation and a "big" version that's able to handle anything up to the 1GB varlena limit. (If you were hoping for documents bigger than that, you'd be needing a couple more orders of magnitude worth of work.) We might also find that there are performance bottlenecks that'd have to be improved, but even just making the code cope with two representations would be a big patch. There has been some cursory talk about this, I think, but I don't believe anyone's actually worked on it since the 2017 patch you mentioned. I'm not sure if that patch is worth using as the basis for a fresh try: it looks like it had some performance issues, and AFAICS it didn't really improve the lexeme-position limit. (Wanders away wondering if the expanded-datum infrastructure could be exploited here...) regards, tom lane
