From: Tim Haak <timh@lucidview.net>
To: pgsql-sql@postgresql.org
Subject: Partitioned tables not using index for min and max 8.2.7?
Date: Wed, 01 Jul 2009 18:42:39 +0200
Message-ID: <4A4B91FF.8040308@lucidview.net> (raw)
Hi
I am running the following query again a partitioned table in 8.2.7. It
does index scans which is unexpected as there are indexes for the
log_date column.
min(log_date) from data.table
"Aggregate (cost=739932.02..739932.02 rows=1 width=8)"
" -> Append (cost=0.00..685106.21 rows=21930321 width=8)"
" -> Seq Scan on table (cost=0.00..33827.10 rows=1215710 width=8)"
" -> Seq Scan on table_yy2009mm03 table (cost=0.00..88056.39
rows=438839 width=8)"
" -> Seq Scan on table_yy2009mm04 table (cost=0.00..204606.67
rows=7344967 width=8)"
" -> Seq Scan on table_yy2009mm05 table (cost=0.00..159210.91
rows=5735091 width=8)"
" -> Seq Scan on table_yy2009mm06 table (cost=0.00..199393.74
rows=7195574 width=8)"
" -> Seq Scan on table_yy2009mm07 table (cost=0.00..11.40
rows=140 width=8)"
though if i run it only agains the one table it is significantly faster
and uses the index
select min(log_date) from only data.table
"Result (cost=0.06..0.07 rows=1 width=0)"
" InitPlan"
" -> Limit (cost=0.00..0.06 rows=1 width=8)"
" -> Index Scan using idx_table_log_date_only on table
(cost=0.00..68272.93 rows=1215710 width=8)"
" Filter: (log_date IS NOT NULL)"
Am I doing something wrong or is this expected.
I tried the old method of
SELECT col FROM table ORDER BY col DESC LIMIT 1
But it does not work either.
--
Tim Haak
Email: timh@lucidview.net
Tel: +27 12 658 9019
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To: pgsql-sql@postgresql.org
Cc: timh@lucidview.net
Subject: Re: Partitioned tables not using index for min and max 8.2.7?
In-Reply-To: <4A4B91FF.8040308@lucidview.net>
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