Questions about TSearch2 and PG 8.2

From: "Markus Wollny" <Markus(dot)Wollny(at)computec(dot)de>
To: <pgsql-general(at)postgresql(dot)org>
Subject: Questions about TSearch2 and PG 8.2
Date: 2007-04-30 17:20:12
Message-ID: 28011CD60FB1724DBA4442E38277F626055F25EF@hermes.computec.de
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Hello!

I'm in the process of upgrading our PostgreSQL 8.1 databases to PostgreSQL 8.2.4. I have stumbled over a minor issue with the upgrade and some helpful suggestions here:
http://people.planetpostgresql.org/xzilla/index.php?/archives/291-The-pain-that-is-tsearch2-8.1-8.2-upgrading.html

I shall try tonight with an plain SQL dump, but as some of my DBs are quite large, I usually use the custom dump format. As I would like to move the tsearch2-stuff in ist own schema as suggested, I tried using a restore list. I'd like to report that everything works as expected, but I've got a slight problem with the custom schema part. I created the target-db, created a schema tsearch2 and installed the tsearch2-functions, operators, configuration and whatnot into this new schema. Then I edited the restore list so that the tsearch2-bits would not be created from the dump file again. However, the binary-dump tries to create the textindex-columns with a tsvector-type which explicitly references the public schema.

Instead of

CREATE TABLE someschema.article
(
id integer,
mytext text,
idxfti tsvector
);

it tries to create the table like this

CREATE TABLE someschema.article
(
id integer,
mytext text,
idxfti public.tsvector
);

As the tsvector-type is defined in the tsearch2-schema, this is bound to fail, even with the search_path set to include the tsearch2-schema. I assume that this happens because the table article is not in the same schema as the original tsvector-type and the default search_path is being ignored on the dump in order to be on the safe side. This "double-checking" breaks the migration in my case, however, so is there some way that would allow me to change the table definition on restore from using just tsvector instead of the explicit public.tsvector? I already tried editing the binary dump, but that just resulted in a corrupted dump-file. I there's no other way, I'll go the plain dump route, of course, but I'd just like to check this issue.

My second question concerns the new Gin (Generalized Inverted Index) index type. Is it stable enough for production yet and would it yield a high enough performance gain in comparison the GiST? Does it make much sense using a Gin-index alongside the GiST-one? Would we need to change anything in the application code in order to make use of Gin - like using

where idxfti @> to_tsquery('default_german', 'Fundstück')

instead of

where idxfti @@ to_tsquery('default_german', 'Fundstück')

? The docs here http://www.sai.msu.su/~megera/wiki/Gin are still a bit thin, so any hint to some further examples would be greatly appreciated.

Kind regards

Markus

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