On Aug 18, 2009, at 6:21 PM, Tom Lane wrote:
What GIN indexes are good for is indexing equality queries on the
components of something the database otherwise thinks of as a single
object. For instance you can GIN-index searches for arrays containing
a particular value as a member.
Now type text doesn't have any built-in notion of a component, other
than individual characters, which aren't normally that interesting
to search for. What I suppose the OP has in mind is full-text
searching, which is looking for component *words*. But "word" is a
very language- and context-dependent concept. And defining which
words
are to be considered equal for searching purposes is even more so.
If we'd hard-wired one notion of "word" into datatype text, it
wouldn't
be very flexible. The point of the tsvector layer is to have a
configurable way to extract searchable words from a chunk of text.
There are also some implementation advantages like not having to
repeat
that processing constantly during a search --- but the main point is
having a place to define what a word is and what search equality
means.
Yes, I was looking for full text searching in english. Since my
postgresql.conf contained:
default_text_search_config = 'pg_catalog.english'
doesn't this specify the parser, dictionary, and template to use for
full text searching in english? I should have mentioned the above in
my post but since it was in the original conf file (debian install) I
didn't think of it.
Bob Gobeille
bobg@xxxxxxxxxxxxx
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