From: Luke Lonergan <llonergan@greenplum.com>
To: Gregory Stark <stark@enterprisedb.com>
To: Mark Kirkwood <markir@paradise.net.nz>
Cc: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Anton <anton200@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: partitioned table and ORDER BY indexed_field DESC LIMIT 1
Date: Wed, 07 Nov 2007 22:40:20 -0800
Message-ID: <C357EF54.44FA2%llonergan@greenplum.com> (raw)
In-Reply-To: <87ode5uujt.fsf@oxford.xeocode.com>
On 11/7/07 10:21 PM, "Gregory Stark" <stark@enterprisedb.com> wrote:
>> part=# explain SELECT * FROM n_traf ORDER BY date_time LIMIT 1;
>> QUERY PLAN
>> -----------------------------------------------------------------------------
>> --------------------------------------------------------------------
>> Limit (cost=198367.14..198367.15 rows=1 width=20)
>> -> Sort (cost=198367.14..200870.92 rows=1001510 width=20)
>> Sort Key: public.n_traf.date_time
>> -> Result (cost=0.00..57464.92 rows=1001510 width=20)
>> -> Append (cost=0.00..57464.92 rows=1001510 width=20)
>> -> Index Scan using n_traf_date_time_login_id on n_traf
>> (cost=0.00..66.90 rows=1510 width=20)
>
> That looks suspicious. There's likely no good reason to be using the index
> scan unless it avoids the sort node above the Append node. That's what I hope
> to do by having the Append executor code do what's necessary to maintain the
> order.
Yah - the way it works in GPDB is that you get a non-sorting plan with an
index scan below the parent - that was the point of the fix. Hmm.
- Luke
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To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, stark@enterprisedb.com, markir@paradise.net.nz, heikki@enterprisedb.com, anton200@gmail.com
Subject: Re: partitioned table and ORDER BY indexed_field DESC LIMIT 1
In-Reply-To: <C357EF54.44FA2%llonergan@greenplum.com>
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