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select query performance question

From: Thomas Zaksek <zaksek(at)ptt(dot)uni-due(dot)de>
To: pgsql-performance(at)postgresql(dot)org
Subject: select query performance question
Date: 2009-07-27 14:09:12
Message-ID: (view raw or flat)
Lists: pgsql-performance
subject is the following type of query needed in a function to select data:

SELECT ' 13.04.2009 12:00:00 ' AS zeit,
'M' AS ganglinientyp,
m.zs_nr AS zs,
de_mw_abh_j_lkw(mw_abh) AS j_lkw,
de_mw_abh_v_pkw(mw_abh) AS v_pkw,
de_mw_abh_v_lkw(mw_abh) AS v_lkw,
de_mw_abh_p_bel(mw_abh) AS p_bel
FROM messungen_v_dat_2009_04_13 m
INNER JOIN de_mw w ON = m.mw_nr
WHERE  m.ganglinientyp = 'M'
AND ' 890 ' = m.minute_tag;
explain analyse brings up 

Nested Loop  (cost=0.00..66344.47 rows=4750 width=10) (actual 
time=134.160..19574.228 rows=4148 loops=1)
   ->  Index Scan using messungen_v_dat_2009_04_13_gtyp_minute_tag_idx 
on messungen_v_dat_2009_04_13 m  (cost=0.00..10749.14 rows=4750 width=8) 
(actual time=64.681..284.732 rows=4148 loops=1)
         Index Cond: ((ganglinientyp = 'M'::bpchar) AND (891::smallint = 
   ->  Index Scan using de_nw_nr_idx on de_mw w  (cost=0.00..10.69 
rows=1 width=10) (actual time=4.545..4.549 rows=1 loops=4148)
         Index Cond: ( = m.mw_nr)
 Total runtime: 19590.078 ms

Seems quite slow to me.
Is this query plan near to optimal or are their any serious flaws?


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Next:From: Tom LaneDate: 2009-07-27 14:18:28
Subject: Re: Can Postgres use an INDEX over an OR?
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Subject: Re: More speed counting rows

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