Horton

Re: On disable_cost

Tomas Vondra <tomas.vondra@2ndquadrant.com>

View thread View on postgr.es
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Jim Finnerty <jfinnert@amazon.com>
Cc: pgsql-hackers@postgresql.org
Date: 2019-11-01T17:04:06Z
Lists: pgsql-hackers 
On Fri, Nov 01, 2019 at 09:30:52AM -0700, Jim Finnerty wrote:
>re: coping with adding disable_cost more than once
>
>Another option would be to have a 2-part Cost structure.  If disable_cost is
>ever added to the Cost, then you set a flag recording this.  If any plans
>exist that have no disable_costs added to them, then the planner chooses the
>minimum cost among those, otherwise you choose the minimum cost path.
>

Yeah, I agree having is_disabled flag, and treat all paths with 'true'
as more expensive than paths with 'false' (and when both paths have the
same value then actually compare the cost) is probably the way forward.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Doc: add detail about EXPLAIN's "Disabled" property

  2. Adjust EXPLAIN's output for disabled nodes

  3. Fix order of parameters in a cost_sort call

  4. Show number of disabled nodes in EXPLAIN ANALYZE output.

  5. Treat number of disabled nodes in a path as a separate cost metric.

  6. Remove grotty use of disable_cost for TID scan plans.