Re: default_text_search_config and expression indexes

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.

>> 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.