> ts_headline uses the original document, not a tsvector summary, so it can > be slow and should be used with care. A typical mistake is to call > ts_headline for every matching document when only ten documents are to be > shown. SQL subqueries can help; here is an example:
I don't see why that stopped being appropriate? The point is that it takes a raw text input which has to be re-parsed; that's still true AFAICS.
I mean that in the past we recommended to use subselect to avoid extra ts_headline() call, which now, at least at 9.6, it's obsoleted and two sql queries call ts_headline() exactly 5 times.
select ts_headline(body,to_tsquery('supernovae & x-ray')),ts_rank(fts,to_tsquery('supernovae & x-ray')) as rank from apod where fts @@ to_tsquery('supernovae & x-ray') order by rank desc limit 5; explain (analyze, costs off) select ts_headline(body,to_tsquery('supernovae & x-ray')), rank from ( select body, ts_rank(fts,to_tsquery('supernovae & x-ray')) as rank from apod where fts @@ to_tsquery('supernovae & x-ray') order by rank desc limit 5 ) as foo;
select ts_headline(body,to_tsquery('supernovae & x-ray')),ts_rank(fts,to_tsquery('supernovae & x-ray')) as rank from apod where fts @@ to_tsquery('supernovae & x-ray') order by rank desc limit 5;
