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To: pgsql-performance@postgresql.org
Subject: Query plan from hell
Date: Fri, 24 Mar 2006 23:54:37 +0100
Message-ID: <op.s6xwlb1mcigqcu@apollo13> (raw )
In-Reply-To: <8427.1143228229@sss.pgh.pa.us >
References: <4423EACD.80706@krap.dk >
<20060324125919.GD90527@pervasive.com >
<5090.1143216154@sss.pgh.pa.us >
<4424458D.4060106@krap.dk >
<8427.1143228229@sss.pgh.pa.us >
Whoa !
bookmark_delta contains very few rows but is inserted/deleted very
often... the effect is spectacular !
I guess I'll have to vacuum analyze this table every minute...
annonces=# EXPLAIN ANALYZE SELECT id, priority FROM annonces WHERE id IN
(SELECT annonce_id FROM bookmark_delta);
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------
Hash IN Join (cost=32.12..8607.08 rows=1770 width=6) (actual
time=387.011..387.569 rows=1 loops=1)
Hash Cond: ("outer".id = "inner".annonce_id)
-> Seq Scan on annonces (cost=0.00..7796.00 rows=101500 width=6)
(actual time=0.022..164.369 rows=101470 loops=1)
-> Hash (cost=27.70..27.70 rows=1770 width=4) (actual
time=0.013..0.013 rows=5 loops=1)
-> Seq Scan on bookmark_delta (cost=0.00..27.70 rows=1770
width=4) (actual time=0.004..0.010 rows=5 loops=1)
Total runtime: 387.627 ms
(6 lignes)
annonces=# EXPLAIN ANALYZE SELECT id, priority FROM annonces a, (SELECT
annonce_id FROM bookmark_delta GROUP BY annonce_id) foo WHERE
a.id=foo.annonce_id;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=32.12..10409.31 rows=1770 width=6) (actual
time=0.081..0.084 rows=1 loops=1)
-> HashAggregate (cost=32.12..49.83 rows=1770 width=4) (actual
time=0.038..0.040 rows=1 loops=1)
-> Seq Scan on bookmark_delta (cost=0.00..27.70 rows=1770
width=4) (actual time=0.024..0.027 rows=5 loops=1)
-> Index Scan using annonces_pkey on annonces a (cost=0.00..5.83
rows=1 width=6) (actual time=0.039..0.040 rows=1 loops=1)
Index Cond: (a.id = "outer".annonce_id)
Total runtime: 0.163 ms
(6 lignes)
annonces=# vacuum bookmark_delta ;
VACUUM
annonces=# EXPLAIN ANALYZE SELECT id, priority FROM annonces WHERE id IN
(SELECT annonce_id FROM bookmark_delta);
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------
Hash IN Join (cost=32.12..8607.08 rows=1770 width=6) (actual
time=195.284..196.063 rows=1 loops=1)
Hash Cond: ("outer".id = "inner".annonce_id)
-> Seq Scan on annonces (cost=0.00..7796.00 rows=101500 width=6)
(actual time=0.014..165.626 rows=101470 loops=1)
-> Hash (cost=27.70..27.70 rows=1770 width=4) (actual
time=0.008..0.008 rows=2 loops=1)
-> Seq Scan on bookmark_delta (cost=0.00..27.70 rows=1770
width=4) (actual time=0.003..0.004 rows=2 loops=1)
Total runtime: 196.122 ms
(6 lignes)
annonces=# vacuum analyze bookmark_delta ;
VACUUM
annonces=# EXPLAIN ANALYZE SELECT id, priority FROM annonces WHERE id IN
(SELECT annonce_id FROM bookmark_delta);
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=1.02..6.88 rows=1 width=6) (actual time=0.025..0.027
rows=1 loops=1)
-> HashAggregate (cost=1.02..1.03 rows=1 width=4) (actual
time=0.011..0.012 rows=1 loops=1)
-> Seq Scan on bookmark_delta (cost=0.00..1.02 rows=2 width=4)
(actual time=0.004..0.006 rows=2 loops=1)
-> Index Scan using annonces_pkey on annonces (cost=0.00..5.83 rows=1
width=6) (actual time=0.009..0.010 rows=1 loops=1)
Index Cond: (annonces.id = "outer".annonce_id)
Total runtime: 0.104 ms
(6 lignes)
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Subject: Re: Query plan from hell
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