alt Hacker NewsThis is really cool. I've built things on PostgreSQL ts_vector() FTS in the past which works well but doesn't have whole-index ranking algorithms so can't do BM25.
It's a bit surprising to me that this doesn't appear to have a mechanism to say "filter for just documents matching terms X and Y, then sort by BM25 relevance" - it looks like this extension currently handles just the BM25 ranking but not the FTS filtering. Are you planning to address that in the future?
I found this example in the README quite confusing:
SELECT * FROM documents
WHERE content <@> to_bm25query('search terms', 'docs_idx') < -5.0
ORDER BY content <@> 'search terms'
LIMIT 10;
I actually don't love this example either, for the reasons you mention, but at some point we had questions about how to filter based on numeric ranking. Thanks for the reminder to revisit this.
Re filtering, there are often reasonable workarounds in the SQL context that caused me to deprioritize this for GA. With your example, the workaround is to apply post-filtering to select just matches with all desired terms. This is not ideal ergonomics since you may have to play with the LIMIT that you'll need to get enough results, but it's already a familiar pattern if you're using vector indexes. For very selective conditions, pre-filtering by those conditions and then ranking afterwards is also an option for the planner, provided you've created indexes on the columns in question.
All this is just an argument about priorities for GA. Now that v1.0 is out, we'll get signal about which features to prioritize next.