Horton

Re: Considering fractional paths in Append node

Andrei Lepikhov <lepihov@gmail.com>

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From: Andrei Lepikhov <lepihov@gmail.com>
To: Nikita Malakhov <hukutoc@gmail.com>, Andy Fan <zhihuifan1213@163.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <dgrowleyml@gmail.com>
Date: 2024-12-06T06:48:48Z
Lists: pgsql-hackers

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  1. Teach Append to consider tuple_fraction when accumulating subpaths.

On 11/2/24 01:18, Nikita Malakhov wrote:
> I've corrected failing test and created a patch at Commitfest:
> https://commitfest.postgresql.org/51/5361/ <https:// 
> commitfest.postgresql.org/51/5361/>
I have played around with this feature, which looks promising for such a 
tiny change. It provides a 'bottom boundary' recommendation for 
appending subpaths, participating in the 'fractional branch' of paths.
As I see it works consistently with the plans, created for plain tables 
filled with similar data.
According to the proposal to change SeqScan logic, IMO, Andy is right. 
But it is a separate improvement because it wouldn't work in the case of 
LIMIT 10 or 100, as the newly added regression tests demonstrate.
I think this feature gives sensible profit for partitionwise paths. 
Pushing this knowledge into subpaths could help postgres_fdw to reduce 
network traffic.

-- 
regards, Andrei Lepikhov