Horton

Re: Consider low startup cost in add_partial_path

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Richard Guo <guofenglinux@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, James Coleman <jtc331@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-02-19T19:29:52Z
Lists: pgsql-hackers

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On Tue, Feb 17, 2026 at 2:44 AM Richard Guo <guofenglinux@gmail.com> wrote:
> Yeah, I agree that we should consider startup cost for partial paths,
> given that cost_gather (and cost_gather_merge) accounts for the
> subpath's startup_cost when calculating the cost of the Gather path.
>
> The changes LGTM.  I noticed one comment that may need to be updated
> accordingly:
>
>  *    As in add_path, the partial_pathlist is kept sorted with the cheapest
>  *    total path in front. ...
>
> This is not true anymore.  The partial_pathlist is now sorted by
> disabled_nodes and then by cheapest total cost.

Thanks. I have committed 0001 after adjusting that comment.

Here's the remaining patch once again. No comments on this one?

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Consider startup cost as a figure of merit for partial paths.

  2. Fix add_partial_path interaction with disabled_nodes

  3. Support parallel joins, and make related improvements.