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optimizing query performance

From: "Frits Hoogland" <frits(dot)hoogland(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: optimizing query performance
Date: 2008-03-31 11:57:08
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hi! I've got the following statement:

             COUNT(sub.os) as total
            SELECT split_part(, ' ', 1) as os
            FROM system, attacks
            WHERE 1 = 1
            AND  timestamp >= 1205708400
            AND timestamp <= 1206313200
            AND attacks.source = system.ip_addr
            AND NOT attacks.source IN (
                    SELECT exclusion
                    FROM org_excl
                    WHERE orgid=2
              ) as sub
             GROUP BY sub.os
             ORDER BY total DESC LIMIT 5

which has the following execution plan:

Limit  (cost=1831417.45..1831417.48 rows=5 width=34) (actual time=
1599.915..1599.925 rows=3 loops=1)
  ->  Unique  (cost=1831417.45..1831417.75 rows=41 width=34) (actualtime=
1599.912..1599.918 rows=3 loops=1)
        ->  Sort  (cost=1831417.45..1831417.55 rows=41 width=34) (actual
time=1599.911..1599.913 rows=3 loops=1)
              Sort Key: count(split_part(("system".name)::text, ''::text,
1)), split_part(("system".name)::text, ' '::text, 1)
              ->  HashAggregate  (cost=1831415.63..1831416.35 rows=41
width=34) (actual time=1599.870..1599.876 rows=3 loops=1)
                    ->  Nested Loop  (cost=23.77..1829328.68 rows=417390
width=34) (actual time=0.075..1474.260 rows=75609 loops=1)
                          ->  Index Scan using index_attacks_timestamp on
attacks  (cost=23.77..2454.92 rows=36300 width=11) (actual time=
0.041..137.045 rows=72380 loops=1)
                                Index Cond: (("timestamp" >= 1205708400) AND
("timestamp" <= 1206313200))
                                Filter: (NOT (hashed subplan))
                                  ->  Seq Scan on org_excl
(cost=0.00..23.75rows=6 width=32) (actual time=
0.014..0.014 rows=0 loops=1)
                                        Filter: (orgid = 2)
                          ->  Index Scan using ip_addr_name_index on
"system"  (cost=0.00..50.15 rows=12 width=45) (actual
time=0.009..0.012rows=1 loops=72380)
                                Index Cond: ("outer".source =

Total runtime: 1600.056 ms

the NL (nested loop) is accountable for most of the total query time. Is
there any way to avoid the NL and/or speed up the query?



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Subject: Re: Bad prepare performance
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Subject: Bad prepare performance

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