Unfortunately, my link to the box with the test database is down due to lack
of maintenance by our local telco (Telstra) but I think that I also missed
the optional config arg to ts_headline.
The lack of link also means that I cannot confirm your findings but your logic
looks good.
It begs the question, however, as to why ts-headline needs to reparse the raw
text.
At least in my case, I am using a trigger to parse the combination of Title
and Abstract to a ts_vector field in the table row (as suggested in 12.2.2
and 12.4.3 in the doco) so that the ts_vector is already available to
ts_headline.
If ts_headline had the ability to use that pre-parsed ts_vector, my problem
would never have arisen - and the performance of ts_headline would be
improved.
Cheers and thanks,
Stephen
On Friday 22 February 2008 20:00, Richard Huxton wrote:
> Stephen Davies wrote:
> > Not quite:-(
> >
> > It is the ts_headline with the explicit "english" configuration that
> > "fails" rather than the implicit "simple".
>
> Hmm... arse.
>
> > That's what is so weird.
> >
> > As you say, the ts_vector has "databas" so the "english" version of
> > ts_headline should work - but it doesn't. The "simple" version does;
> > despite the above.
>
> [goes away, tests some more]
>
> OK, so:
>
> set default_text_search_config = 'simple';
> SELECT ts_headline('my database is a database', to_tsquery('database'));
> SELECT ts_headline('my database is a database', to_tsquery('simple',
> 'database'));
> SELECT ts_headline('my database is a database', to_tsquery('english',
> 'database'));
>
> The first two work, the last one doesn't.
>
> set default_text_search_config = 'english';
> SELECT ts_headline('my database is a database', to_tsquery('database'));
> SELECT ts_headline('my database is a database', to_tsquery('simple',
> 'database'));
> SELECT ts_headline('my database is a database', to_tsquery('english',
> 'database'));
>
> The middle one doesn't work.
>
> Note that there are no indexes involved here, we're just running against
> the raw text.
>
> [light goes on over sluggish London-based database chap]
>
> When the ts_headline function is working on the text, it needs to
> convert it from varchar/text type to tsvector so that it can use the
> tsquery to find words to highlight.
>
> When it converts the text to a tsvector, it's doing it based on
> default_text_search_config - we've not told it otherwise. In an ideal
> world, it would look "inside" the tsquery and see what config that was
> using, but it can't (or at least doesn't).
>
> Of course, if to_tsquery()'s config doesn't match to_tsheadline()'s then
> we get a problem.
>
> And, if I actually bother to read an up-to-date copy of the manual,
> rather than the beta version I've got linked on my desktop I can see
> there's a parameter for ts_headline. So...
>
> set default_text_search_config = 'simple';
> SELECT ts_headline('english', 'my database is a database',
> to_tsquery('english','database')
> );
>
> set default_text_search_config = 'english';
> SELECT ts_headline('simple', 'my database is a database',
> to_tsquery('simple','database')
> );
>
>
> These all work fine. Phew!
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