Message-ID: <434A6C2D.9070207@liveye.net>
Date: Mon, 10 Oct 2005 15:27:09 +0200
From: "Federico Simonetti (Liveye)" <federico@liveye.net>
User-Agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)
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To: pgsql-performance@postgresql.org
Subject: Query performance on ILIKE with AND operator...
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Hello all,

I'm encountering a quite strange performance problem. Look at the
following two queries and their execution times. The only difference is
the first query has OR operator and the second query has AND operator.
Any ideas?

Thank you in advance,
Federico


[FIRST QUERY: EXEC TIME 0.015 SECS]

    explain analyze SELECT * FROM ViewHttp
    WHERE txContentType ilike '%html%' OR vchost ilike '%www.%'
    ORDER BY iDStart DESC, iS_ID DESC, iF_ID DESC, iSubID DESC
    OFFSET 0 LIMIT 201

"Limit  (cost=12.75..3736.66 rows=201 width=1250) (actual
time=0.000..15.000 rows=201 loops=1)"
"  ->  Nested Loop  (cost=12.75..1996879.04 rows=107782 width=1250)
(actual time=0.000..15.000 rows=201 loops=1)"
"        ->  Nested Loop  (cost=12.75..1524883.03 rows=6334 width=1106)
(actual time=0.000..15.000 rows=201 loops=1)"
"              Join Filter: ("outer".isensorid = "inner".isensorid)"
"              ->  Index Scan Backward using idx_0009_ord4 on
detail0009  (cost=0.00..1489241.53 rows=6334 width=1005) (actual
time=0.000..15.000 rows=201 loops=1)"
"                    Filter: ((txcontenttype ~~* '%html%'::text) OR
((vchost)::text ~~* '%www.%'::text))"
"              ->  Materialize  (cost=12.75..15.25 rows=250 width=101)
(actual time=0.000..0.000 rows=1 loops=201)"
"                    ->  Seq Scan on sensors  (cost=0.00..12.50 rows=250
width=101) (actual time=0.000..0.000 rows=1 loops=1)"
"        ->  Index Scan using connections_pkey on connections 
(cost=0.00..74.25 rows=18 width=168) (actual time=0.000..0.000 rows=1
loops=201)"
"              Index Cond: (("outer".is_id = connections.is_id) AND
("outer".if_id = connections.if_id))"
"Total runtime: 15.000 ms"


[SECOND QUERY: EXEC TIME 13.844 SECS]

    explain analyze SELECT * FROM ViewHttp
    WHERE txContentType ilike '%html%' AND vchost ilike '%www.%'
    ORDER BY iDStart DESC, iS_ID DESC, iF_ID DESC, iSubID DESC
    OFFSET 0 LIMIT 201

"Limit  (cost=22476.81..22477.31 rows=201 width=1250) (actual
time=13187.000..13187.000 rows=201 loops=1)"
"  ->  Sort  (cost=22476.81..22477.92 rows=443 width=1250) (actual
time=13187.000..13187.000 rows=201 loops=1)"
"        Sort Key: detail0009.idstart, detail0009.isensorid,
detail0009.iforensicid, detail0009.isubid"
"        ->  Hash Join  (cost=13.13..22457.34 rows=443 width=1250)
(actual time=469.000..10966.000 rows=53559 loops=1)"
"              Hash Cond: ("outer".isensorid = "inner".isensorid)"
"              ->  Nested Loop  (cost=0.00..22437.57 rows=443
width=1165) (actual time=469.000..10201.000 rows=53559 loops=1)"
"                    ->  Seq Scan on detail0009  (cost=0.00..20500.11
rows=26 width=1005) (actual time=453.000..5983.000 rows=53588 loops=1)"
"                          Filter: ((txcontenttype ~~* '%html%'::text)
AND ((vchost)::text ~~* '%www.%'::text))"
"                    ->  Index Scan using connections_pkey on
connections  (cost=0.00..74.25 rows=18 width=168) (actual
time=0.063..0.065 rows=1 loops=53588)"
"                          Index Cond: (("outer".isensorid =
connections.isensorid) AND ("outer".iforensicid = connections.iforensicid))"
"              ->  Hash  (cost=12.50..12.50 rows=250 width=101) (actual
time=0.000..0.000 rows=0 loops=1)"
"                    ->  Seq Scan on sensors  (cost=0.00..12.50 rows=250
width=101) (actual time=0.000..0.000 rows=1 loops=1)"
"Total runtime: 13844.000 ms"