Denis,
we need examples of your explain analyze. I don't want to waste my time
reading theoretical reasoning :)
btw, Be sure you use the same search configuration as in create index or
index will not be used at all.
Oleg
On Wed, 25 Aug 2010, Denis Papathanasiou wrote:
As a follow-up to my question from this past Saturday
(http://archives.postgresql.org/pgsql-general/2010-08/msg00624.php), I
experimented with adding two types of indices to the same text column:
CREATE INDEX item_eng_searchable_text_idx ON item USING
gin(to_tsvector('english', searchable_text));
and
CREATE INDEX item_searchable_text_idx ON item (searchable_text);
Running my queries under explain, I noticed that queries of the form:
select pk from item where searchable_text @@ plainto_tsquery('search
phrase');
Actually run *slower* with the item_eng_searchable_text_idx index applied.
But when I switch the query to use to_tsquery() instead, e.g. something
like this:
select pk from item where searchable_text @@ to_tsquery('phrase');
The performance is better.
Is this because the gin/to_tsvector() index works differently for
to_tsquery() compared to plainto_ts_query() ?
If so, how can I create an effective index for queries that will use
plainto_tsquery() ?
Note that I need the plainto_tsquery() form b/c my search phrases will
correspond to exact blocks of text, and therefore they will contain
spaces and punctuation, etc.
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: o...@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83
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