From: Kyle Bateman <kyle@actarg.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-sql@postgresql.org
Subject: Re: Using bitmap index scans-more efficient
Date: Wed, 16 Aug 2006 14:46:06 -0600
Message-ID: <44E3840E.4080502@actarg.com> (raw)
In-Reply-To: <26676.1155747492@sss.pgh.pa.us>
References: <44DF6582.4000806@actarg.com>
<82mza77rch.fsf@mid.bfk.de>
<44E11E1A.8020507@actarg.com>
<27367.1155606817@sss.pgh.pa.us>
<44E349BA.4070205@actarg.com>
<26676.1155747492@sss.pgh.pa.us>
Tom Lane wrote:
>Kyle Bateman <kyle@actarg.com> writes:
>
>
>>I'm wondering if this might expose a weakness in the optimizer having to
>>do with left joins.
>>
>>
>
>Before 8.2 the optimizer has no ability to rearrange the order of outer
>joins. Do you have time to try your test case against CVS HEAD?
>
>
OK, I figured it out--grabbed the latest snapshot (hope that is what you
need).
My results are similar:
select l.* from ledg_v1 l, proj p where l.proj = p.proj_id and 5 =
p.par; (24 msec)
Nested Loop (cost=0.00..1991.93 rows=480 width=23)
-> Nested Loop (cost=0.00..4.68 rows=6 width=8)
-> Seq Scan on acct a (cost=0.00..1.12 rows=1 width=4)
Filter: ((code)::text = 'ap'::text)
-> Index Scan using i_proj_par on proj p (cost=0.00..3.49
rows=6 width=4)
Index Cond: (5 = par)
-> Index Scan using i_ledg_proj on ledg l (cost=0.00..330.17
rows=83 width=19)
Index Cond: (l.proj = "outer".proj_id)
select l.* from ledg_v2 l, proj p where l.proj = p.proj_id and 5 =
p.par; (1.25 sec)
Hash Join (cost=4.63..16768.43 rows=480 width=23)
Hash Cond: ("outer".proj = "inner".proj_id)
-> Nested Loop Left Join (cost=1.13..14760.13 rows=400000 width=23)
-> Seq Scan on ledg l (cost=0.00..6759.00 rows=400000 width=19)
-> Materialize (cost=1.13..1.14 rows=1 width=4)
-> Seq Scan on acct a (cost=0.00..1.12 rows=1 width=4)
Filter: ((code)::text = 'ap'::text)
-> Hash (cost=3.49..3.49 rows=6 width=4)
-> Index Scan using i_proj_par on proj p (cost=0.00..3.49
rows=6 width=4)
Index Cond: (5 = par)
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To: pgsql-sql@postgresql.org
Cc: kyle@actarg.com, tgl@sss.pgh.pa.us
Subject: Re: Using bitmap index scans-more efficient
In-Reply-To: <44E3840E.4080502@actarg.com>
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