Re: [HACKERS] Corner case for add_path_precheck

2015-02-11 Thread Tom Lane
Antonin Houska a...@cybertec.at writes:
 Tom Lane t...@sss.pgh.pa.us wrote:
 Antonin Houska a...@cybertec.at writes:
 The special case is that the path passed to add_path_precheck() has costs
 *equal to* those of the old_path. If pathkeys, outer rells and costs are the
 same, as summarized in the comment above, I expect add_path_precheck() to
 return false. Do I misread anything?

 It does, so I don't see your point?

 Just that pre-check is - in this special (and very rare?) case - more
 stringent than the proper check would be.

It's assuming that a nonzero amount of cost will be added on before the
real check happens.  Even if none was added, discarding the new path is
the way we'd break the tie that would result, so I still don't see your
point.

regards, tom lane


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers


Re: [HACKERS] Corner case for add_path_precheck

2015-02-11 Thread Antonin Houska
Tom Lane t...@sss.pgh.pa.us wrote:
 Antonin Houska a...@cybertec.at writes:
  The special case is that the path passed to add_path_precheck() has costs
  *equal to* those of the old_path. If pathkeys, outer rells and costs are the
  same, as summarized in the comment above, I expect add_path_precheck() to
  return false. Do I misread anything?
 
 It does, so I don't see your point?

Just that pre-check is - in this special (and very rare?) case - more
stringent than the proper check would be.

-- 
Antonin Houska
Cybertec Schönig  Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de, http://www.cybertec.at


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers


Re: [HACKERS] Corner case for add_path_precheck

2015-02-10 Thread Tom Lane
Antonin Houska a...@cybertec.at writes:
 The special case is that the path passed to add_path_precheck() has costs
 *equal to* those of the old_path. If pathkeys, outer rells and costs are the
 same, as summarized in the comment above, I expect add_path_precheck() to
 return false. Do I misread anything?

It does, so I don't see your point?

regards, tom lane


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers