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Re: Consider low startup cost in add_partial_path - Mailing list pgsql-hackers

From Richard Guo
Subject Re: Consider low startup cost in add_partial_path
Date
Msg-id CAMbWs4-mO3jMK4t_LgcJ+7Eo=NmGgkxettgRaVbJzZvVZ1koMA@mail.gmail.com
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In response to Re: Consider low startup cost in add_partial_path  (Robert Haas <robertmhaas@gmail.com>)
Responses Re: Consider low startup cost in add_partial_path
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On Sat, Feb 7, 2026 at 6:06 AM Robert Haas <robertmhaas@gmail.com> wrote:
> I rediscovered this problem while testing pg_plan_advice, and I think
> we should commit something to fix it.

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.

- Richard

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