Horton

Re: Considering fractional paths in Append node

Andy Fan <zhihuifan1213@163.com>

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From: Andy Fan <zhihuifan1213@163.com>
To: Nikita Malakhov <hukutoc@gmail.com>
Cc: Andrei Lepikhov <lepihov@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, David Rowley <dgrowleyml@gmail.com>
Date: 2024-10-17T23:36:37Z
Lists: pgsql-hackers

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  1. Teach Append to consider tuple_fraction when accumulating subpaths.

Nikita Malakhov <hukutoc@gmail.com> writes:

> Hi,
>
> Andy, your words make sense, but to me it seems that in add_paths_to_append_rel
> we have no other options than tuple_fraction from root, and rows (if any) in paths
> we take into account, please correct me if I am wrong.

One of the option might be applying your logic only if we can prove the
tuple_fraction from root is same as the tuple_fraction, similar with
what I did before. But it is proved that is too complex. 

> Thank you!
>
> Also, on top of that I have an idea of pruning unnecessary partitions
> in generate_orderedappend_paths() when we have a valid LIMIT value.
> I'm currently checking if it is working correctly in multiple cases,
> so 'll send it after we deal with this issue.

-- 
Best Regards
Andy Fan