slow count() was: tsearch2 poor performance

On Fri, 1 Oct 2004, Kris Kiger wrote:

> Hey all, its me again. If I do not do a count(product_id) on my
> tsearch2 queries, its actually really fast, for example;
>

Hmm, I also really want to know what's the difference ?
Postgresql 8.0beta3 on Linux 2.4.25

tsearchd=# explain analyze select body from txt where fts_index @@ to_tsquery('oil') limit 1000;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..4027.67 rows=1000 width=315) (actual time=0.053..14.662 rows=1000 loops=1)
-> Index Scan using fts_idx on txt (cost=0.00..12083.02 rows=3000 width=315) (actual time=0.049..12.552 rows=1000 loops=1)
Index Cond: (fts_index @@ '\'oil\''::tsquery)
Total runtime: 15.848 ms
(4 rows)

tsearchd=# explain analyze select count(body) from txt where fts_index @@ to_tsquery('oil') limit 1000;

Didn't get result after 10 minutes :(

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
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