Re: Proof of concept for MIN/MAX optimization

From: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Proof of concept for MIN/MAX optimization
Date: 2005-04-14 04:11:13
Message-ID: 425DED61.5080104@paradise.net.nz
Views: Raw Message | Whole Thread | Download mbox
Thread:
Lists: pgsql-patches

Tom Lane wrote:
> I haven't done the work yet to add a column to pg_aggregate, so this
> just knows about optimizing a couple of hard-wired cases (int4 and
> text). Other than that it's reasonably complete, I think. Comments?
>

Looks good :

regression=# explain select max(unique1) from tenk1;
QUERY PLAN
---------------------------------------------------------------------------------------------------------
Result (cost=0.15..0.16 rows=1 width=0)
InitPlan
-> Limit (cost=0.00..0.15 rows=1 width=4)
-> Index Scan Backward using tenk1_unique1 on tenk1
(cost=0.00..1512.59 rows=10000 width=4)
(4 rows)

The handling of nulls is a little unexpected (still todo?) :

regression=# insert into tenk2 (unique1,unique2) values(null, 10000);
INSERT 0 1
regression=# select max(unique1) from tenk2;
max
-----

(1 row)
regression=# set enable_indexscan=0;
SET
regression=# select max(unique1) from tenk2;
max
------
9999
(1 row)

cheers

Mark

In response to

Responses

Browse pgsql-patches by date

  From Date Subject
Next Message Tom Lane 2005-04-14 06:58:12 Re: Proof of concept for MIN/MAX optimization
Previous Message Greg Sabino Mullane 2005-04-13 01:22:33 Re: Remove unneeded left joins from psql