Re: text search: restricting the number of parsed words in headline generation

I will do the profiling and present the results.

On Wed, 2012-08-15 at 12:45 -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Is this a TODO?
> 
> AFAIR nothing's been done about the speed issue, so yes.  I didn't
> like the idea of creating a user-visible knob when the speed issue
> might be fixable with internal algorithm improvements, but we never
> followed up on this in either fashion.
> 
>             regards, tom lane
> 
> > ---------------------------------------------------------------------------
> 
> > On Tue, Aug 23, 2011 at 10:31:42PM -0400, Tom Lane wrote:
> >> Sushant Sinha <sushant354@gmail.com> writes:
> >>> Doesn't this force the headline to be taken from the first N words of
> >>> the document, independent of where the match was?  That seems rather
> >>> unworkable, or at least unhelpful.
> >> 
> >>> In headline generation function, we don't have any index or knowledge of
> >>> where the match is. We discover the matches by first tokenizing and then
> >>> comparing the matches with the query tokens. So it is hard to do
> >>> anything better than first N words.
> >> 
> >> After looking at the code in wparser_def.c a bit more, I wonder whether
> >> this patch is doing what you think it is.  Did you do any profiling to
> >> confirm that tokenization is where the cost is?  Because it looks to me
> >> like the match searching in hlCover() is at least O(N^2) in the number
> >> of tokens in the document, which means it's probably the dominant cost
> >> for any long document.  I suspect that your patch helps not so much
> >> because it saves tokenization costs as because it bounds the amount of
> >> effort spent in hlCover().
> >> 
> >> I haven't tried to do anything about this, but I wonder whether it
> >> wouldn't be possible to eliminate the quadratic blowup by saving more
> >> state across the repeated calls to hlCover().  At the very least, it
> >> shouldn't be necessary to find the last query-token occurrence in the
> >> document from scratch on each and every call.
> >> 
> >> Actually, this code seems probably flat-out wrong: won't every
> >> successful call of hlCover() on a given document return exactly the same
> >> q value (end position), namely the last token occurrence in the
> >> document?  How is that helpful?
> >> 
> >> regards, tom lane
> >> 
> >> -- 
> >> Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
> >> To make changes to your subscription:
> >> http://www.postgresql.org/mailpref/pgsql-hackers
> 
> > -- 
> >   Bruce Momjian  <bruce@momjian.us>        http://momjian.us
> >   EnterpriseDB                             http://enterprisedb.com
> 
> >   + It's impossible for everything to be true. +
> 
> 
> > -- 
> > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
> > To make changes to your subscription:
> > http://www.postgresql.org/mailpref/pgsql-hackers