Re: default_text_search_config and expression indexes

Ron Mayer wrote:
> Bruce Momjian wrote:
> > Oleg Bartunov wrote:
> >> What is a basis of your assumption ? In my opinion, it's very limited
> >> use of text search, because it doesn't supports ranking. For 4-5 years
> >> of tsearch2 usage I never used it and I never seem in mailing lists.
> >> This is very user-oriented feature and we could probably ask
> >> -general people for their opinion.
>
> I think I asked about this kind of usage a couple years back;
> and Oleg pointed out other reasons why it wasn't as good an
> idea too.
>
> http://archives.postgresql.org/pgsql-general/2005-10/msg00475.php
> http://archives.postgresql.org/pgsql-general/2005-10/msg00477.php
>
> The particular question I had asked why the functional index was
> slower than maintaining the extra column; with the explanation
> that the lossy index having to call the function (including
> parsing, dictionary lookup, etc) for re-checking the data made
> it inadvisable to avoid the extra column anyway.
>
> > I doubt 'general' is going to understand the details of merging this
> > into the backend. I assume we have enough people on hackers to decide
> > this.
> >
> > Are you saying the majority of users have a separate column with a
> > trigger?
>
> I think so. At least when I was using it in 2005 the second
> column with the trigger was faster than using a functional index.

OK, it is good you measured it. I wonder how GIN would behave because
it is not lossy.

> >> We need more feedback from users.
> >
> > Well, I am waiting for other hackers to get involved, but if they don't,
> > I have to evaluate it myself on the email lists.
>
> Personally, I think documentation changes would be an OK way to
> to handle it. Something that makes it extremely clear to the
> user the advantages of having the extra column and the risks
> of avoiding them.

Sure, but you have make sure you use the right configuration in the
trigger, no? Does the tsquery have to use the same configuration?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

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