Re: 500rows = 1min/2.5k rows=20min/6K rows 2 hours and still running

sorry.. I sent this as I was about to go to bed and the explain analyse
of the query w/ 4 tables joined per subquery came out.

So.. attaching it..

On Wed, 2007-09-12 at 00:57 +0800, El-Lotso wrote:
> Hi,
>
> appreciate if someone can have some pointers for this.
>
> PG.8.2.4 1.4G centrino(s/core) 1.5GB ram/5400rpm laptop HD
>
> 3 mail tables which has already been selected "out" into separate tables
> (useing create table foo as select * from foo_main where x=y)
>
> These test tables containing only a very small subset of the main data's
> table (max 1k to 10k rows vs 1.5mill to 7mill rows in the main table)
>
> table definitions and actual query are attached. (names has been altered
> to protect the innocent)
>
> I've played around with some tweaking of the postgres.conf setting per
> guidance from jdavis (in irc) w/o much(any) improvement. Also tried
> re-writing the queries to NOT use subselects (per depesz in irc also)
> also yielded nothing spectacular.
>
> The only thing I noticed was that when the subqueries combine more than
> 3 tables, then PG will choke. If only at 3 joined tables per subquery,
> the results come out fast, even for 6K rows.
>
> but if the subqueries (these subqueries by itself, executes fast and
> returns results in 1 to 10secs) were done independently and then placed
> into a temp table, and then finally joined together using a query such
> as
>
> select a.a,b.b,c.c from a inner join b on (x = x) left outer join c on(x
> = y)
>
> then it would also be fast
>
> work_mem = 8MB / 32MB /128MB (32 MB default in my setup)
> effective_Cache_size = 128MB/500MB (500 default)
> shared_buffers = 200MB
> geqo_threshold = 5 (default 12)
> geqo_effort = 2 (default 5)
> ramdom_page_cose = 8.0 (default 4)
> maintenance_work_mem = 64MB
> join_collapse_limit = 1/8/15 (8 default)
> from_collapse_limit = 1/8/15 (8 default)
> enable_nestloop = f (on by default)
>
> based on current performance, even with a small number of rows in the
> individual tables (max 20k), I can't even get a result out in 2 hours.
> (> 3 tables joined per subquery) which is making me re-think of PG's
> useful-ness.
>
>
>
> BTW, I also tried 8.2.4 CVS_STABLE Branch