Horton

Re: On disable_cost

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Richard Guo <guofenglinux@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <dgrowleyml@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-09-06T10:10:10Z
Lists: pgsql-hackers 
Hello Richard,

06.09.2024 12:51, Richard Guo wrote:
> Ah I see.  label_sort_with_costsize is only used to label the Sort
> node nicely for EXPLAIN, and usually we do not display the cost
> numbers in regression tests.

In fact, I see the error with the following (EXPLAIN-less) query:
create table t (x int);

select * from t natural inner join
(select * from (values(1)) v(x)
   union all
  select 1 from t t1 full join t t2 using (x),
                t t3 full join t t4 using (x)
);

2024-09-06 10:01:48.034 UTC [696535:5] psql LOG:  statement: select * from t natural inner join
     (select * from (values(1)) v(x)
       union all
      select 1 from t t1 full join t t2 using (x),
                    t t3 full join t t4 using (x)
     );
createplan.c:5457:6: runtime error: 4.99254e+09 is outside the range of representable values of type 'int'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior createplan.c:5457:6 in

(An UBSan-enabled build --with-blocksize=32 is required for this query to
trigger the failure.)

Best regards,
Alexander

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.