Horton

Re: On disable_cost

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-08-21T14:29:23Z
Lists: pgsql-hackers 
On Fri, Aug 2, 2024 at 12:53 PM Robert Haas <robertmhaas@gmail.com> wrote:
> On Fri, Aug 2, 2024 at 12:51 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > That absolutely is the expectation, and we'd better be careful not
> > to break it.
>
> I have every intention of not breaking it. :-)

I went ahead and committed these patches. I know there's some debate
over whether we want to show the # of disabled nodes and if so whether
it should be controlled by COSTS, and I suspect I haven't completely
allayed David's concerns about the initial_cost_XXX functions although
I think that I did the right thing. But, I don't have the impression
that anyone is desperately opposed to the basic concept, so I think it
makes sense to put these into the tree and see what happens. We have
quite a bit of time left in this release cycle to uncover bugs, hear
from users or other developers, etc. about what problems there may be
with this. If we end up deciding to reverse course or need to fix a
bunch of stuff, so be it, but let's see what the feedback is.

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

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.