Re: Tsearch2 performance on big database - Mailing list pgsql-performance

On Tue, 22 Mar 2005 14:25:19 +0100, Rick Jansen <rick@rockingstone.nl> wrote:
>
> ilab=# explain analyze select count(titel) from books where idxfti @@
> to_tsquery('default', 'buckingham | palace');
>                                                                 QUERY PLAN
>
----------------------------------------------------------------------------------------------------------------------------------------
>   Aggregate  (cost=35547.99..35547.99 rows=1 width=56) (actual
> time=125968.119..125968.120 rows=1 loops=1)
>     ->  Index Scan using idxfti_idx on books  (cost=0.00..35525.81
> rows=8869 width=56) (actual time=0.394..125958.245 rows=3080 loops=1)
>           Index Cond: (idxfti @@ '\'buckingham\' | \'palac\''::tsquery)
>   Total runtime: 125968.212 ms
> (4 rows)
>
> Time: 125969.264 ms
> ilab=#

Ahh... I should have qualified my claim.  I am creating a google-esqe
search interface and almost every query uses '&' as the term joiner.
'AND' queries and one-term queries are orders of magnitude faster than
'OR' queries, and fortunately are the expected default for most users.
 (Think, "I typed in these words, therefore I want to match these
words"...)  An interesting test may be to time multiple queries
independently, one for each search term, and see if the combined cost
is less than a single 'OR' search.  If so, you could use UNION to join
the results.

However, the example you originally gave ('terminology') should be
very fast.  On a comparable query ("select count(value) from
metabib.full_rec where index_vector @@ to_tsquery('default','jane');")
I get 12ms.

Oleg, do you see anything else on the surface here?

Try:

EXPLAIN ANALYZE
  SELECT titel FROM books WHERE idxfti @@
    to_tsquery('default', 'buckingham')
  UNION
  SELECT titel FROM books WHERE idxfti @@
    to_tsquery('default', 'palace');

and see if using '&' instead of '|' where you can helps out.  I
imagine you'd be surprised by the speed of:

  SELECT titel FROM books WHERE idxfti @@
    to_tsquery('default', 'buckingham&palace');


>
>  > As an example of what I think you *should* be seeing, I have a similar
>  > box (4 procs, but that doesn't matter for one query) and I can search
>  > a column with tens of millions of rows in around a second.
>  >
>
> That sounds very promising, I'd love to get those results.. could you
> tell me what your settings are, howmuch memory you have and such?

16G of RAM on a dedicated machine.


shared_buffers = 15000          # min 16, at least max_connections*2, 8KB each
work_mem = 10240                # min 64, size in KB
maintenance_work_mem = 1000000  # min 1024, size in KB
# big m_w_m for loading data...

random_page_cost = 2.5          # units are one sequential page fetch cost
# fast drives, and tons of RAM


--
Mike Rylander
mrylander@gmail.com
GPLS -- PINES Development
Database Developer
http://open-ils.org