Re: Join Query Perfomance Issue

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We have tried some recoding now, using a materialized view we could reduce the query to a join over too tables without any functions inside the query, for example:

explain analyse SELECT '12.11.2007 18:04:00 UTC' AS zeit,
                      'M' AS ganglinientyp,
                      zs_de,
                  j_ges,
                      j_lkw,
                      v_pkw,
                      v_lkw,
                  p_bel
                  FROM  messungen_v_dat_2007_11_12 m
                      LEFT JOIN messwerte_mv w on w.nr = m.messpunkt
WHERE m.ganglinientyp = 'M' AND 992 = m.minute_tag;

Nested Loop Left Join (cost=0.00..32604.48 rows=3204 width=14) (actual time=11.991..2223.227 rows=2950 loops=1) -> Index Scan using messungen_v_dat_2007_11_12_messpunkt_minute_tag_idx on messungen_v_dat_2007_11_12 m (cost=0.00..5371.09 rows=3204 width=4) (actual time=0.152..12.385 rows=2950 loops=1)
        Index Cond: ((ganglinientyp = 'M'::bpchar) AND (992 = minute_tag))
-> Index Scan using messwerte_mv_nr_idx on messwerte_mv w (cost=0.00..8.49 rows=1 width=18) (actual time=0.730..0.734 rows=1 loops=2950)
        Index Cond: (w.nr = m.messpunkt)
Total runtime: 2234.143 ms
(6 rows)

To me this plan looks very clean and nearly optimal, BUT ~2seconds for the nested loop can't be that good, isn't it? The behavior of this query and the database is quite a mystery for me, yesterday i had it running in about 100ms, today i started testing with the same query and 2000-3000ms :(

Could this be some kind of a postgresql server/configuration problem? This queries are very perfomance dependend, they are called a lot of times in a comlex physical real time simulation of traffic systems. 200ms would be ok here, but >1sec is perhaps not functional.

The old version just used one big (partitioned) table without any joins, performing this query in 10-300ms, depended on the server load.

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