Horton

Re: On disable_cost

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Zhenghua Lyu <zlv@pivotal.io>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-11-01T16:00:38Z
Lists: pgsql-hackers 
Hi,

On 2019-11-01 19:58:04 +1300, Thomas Munro wrote:
> On Fri, Nov 1, 2019 at 7:42 PM Zhenghua Lyu <zlv@pivotal.io> wrote:
> >     It is tricky to set disable_cost a huge number. Can we come up with better solution?
> 
> What happens if you use DBL_MAX?

That seems like a bad idea - we add the cost multiple times. And we
still want to compare plans that potentially involve that cost, if
there's no other way to plan the query.

- Andres

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.