Re: min/max planner optimization - Mailing list pgsql-hackers

From Gregory Stark
Subject Re: min/max planner optimization
Date
Msg-id 87lk9ozjp1.fsf@oxford.xeocode.com
Whole thread Raw
In response to Re: min/max planner optimization  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: min/max planner optimization
List pgsql-hackers
"Tom Lane" <tgl@sss.pgh.pa.us> writes:

> The only case where the optimization is a win is where you have a
> zero-startup-cost subplan, and the only way to get sorted output with zero
> startup cost is an indexscan.

Sure but there could be other nodes above the index scan which preserve the
order. In particular nested loop and merge joins. Unique also preserves the
order but I can't see how it could be useful here. And of course potentially
Append nodes in the future...

--  Gregory Stark EnterpriseDB          http://www.enterprisedb.com


pgsql-hackers by date:

Previous
From: "Pavel Stehule"
Date:
Subject: Re: Proposal: real procedures again (8.4)
Next
From: Tom Lane
Date:
Subject: Re: Datum should be defined outside postgres.h