Re: [GENERAL] TSearch2: find a QUERY that does match a single document

On Fri, 12 Sep 2008, Dmitry Koterov wrote:

> Hello.
>
> TSearch2 allows to search a table of tsvectors by a single tsquery.
> I need to solve the reverse problem.
>
> *I have a large table of tsquery. I need to find all tsqueries in that table
> that match a single document tsvector:
> *
> CREATE TABLE "test"."test_tsq" (
> "id" SERIAL,
> "q" TSQUERY NOT NULL,
> CONSTRAINT "test_tsq_pkey" PRIMARY KEY("id")
> );
>
> insert into test.test_tsq(q)
> select to_tsquery(g || 'x' || g) from generate_series(100000, 900000) as g;
>
> explain analyze
> select * from test.test_tsq
> where to_tsvector('400000x400000') @@ q

why do you need tsvector @@ q ? Much better to use tsquery = tsquery

test=# explain analyze select * from test_tsq where q = '400000x400000'::tsque>
QUERY PLAN
-----------------------------------------------------------------------------------------------------------
Seq Scan on test_tsq (cost=0.00..16667.01 rows=1 width=38) (actual time=129.208..341.111 rows=1 loops=1)
Filter: (q = '''400000x400000'''::tsquery)
Total runtime: 341.134 ms
(3 rows)

Time: 341.478 ms

>
> This gets a strange explain analyze:
>
> QUERY PLAN
> Seq Scan on test_tsq (cost=0.00..17477.01 rows=800 width=36) (actual
> time=68.698..181.458 rows=1 loops=1)
> Filter: ('''400000x400000'':1'::tsvector @@ q)
> Total runtime: 181.484 ms
>
> No matter if I use GIST index on test_tsq.q or not: the explain analyze
> result is the same.
> So, why "rows=800"? The table contains much more rows...

'800' is the number of estimated rows, which is not good, since you got only
1 row.

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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