Thread

1. Precheck to consider path costs for partial paths

   Nikita Malakhov <hukutoc@gmail.com> — 2024-12-03T18:24:37Z

   Hi hackers!
   
   I'd stumbled upon the discussion [1] on TPC-DS query performance,
   looked into code that caused this behavior and saw that partial hash,
   merge and nested loop paths are discarded regardless of costs
   if they have more pathkeys.
   
   I've excluded the pathkey chain length condition from the precheck function
   and added passing precalculated startup cost in addition to total cost,
   and it seems to produce a more effective plan for case in [1].
   
   Please check the attached patch. I'm very interested if my assumption
   is correct or not.
   
   [1]
   https://www.postgresql.org/message-id/flat/SEZPR06MB649422CDEBEBBA3915154EE58A232%40SEZPR06MB6494.apcprd06.prod.outlook.com
   
   -- 
   Regards,
   Nikita Malakhov
   Postgres Professional
   The Russian Postgres Company
   https://postgrespro.ru/
   

2. Re: Precheck to consider path costs for partial paths

   Andreas Karlsson <andreas@proxel.se> — 2024-12-16T03:35:50Z

   On 12/3/24 7:24 PM, Nikita Malakhov wrote:
   > Please check the attached patch. I'm very interested if my assumption
   > is correct or not.
   
   Hi,
   
   You probably attached the wrong file since your patch does not even compile.
   
   Andreas