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Date: Tue, 4 Nov 2025 14:43:05 +0100
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Subject: Re: BUG #19102: Assertion failure in generate_orderedappend_paths
 with aggregate pushdown
To: Richard Guo <guofenglinux@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org, akorotkov@postgresql.org,
 Kuntal Ghosh <kuntalghosh.2007@gmail.com>
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From: Andrei Lepikhov <lepihov@gmail.com>
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On 4/11/2025 08:44, Richard Guo wrote:
> Any thoughts?The first patch looks good, but I still have a couple of questions.
1. We don't use parameterised paths in MergeAppend yet. I wonder if it 
could be nudged by spreading the use of partitioned tables with foreign 
partitions. Do you think, in such a case, the usage of 
cheapest_total->rows will stay correct? It seems that the parameterised 
path has much less estimation than the RelOptInfo...

2. I understand why the upper relation has unset nrows. However, it may 
be more accurate to set row estimation for a pushing-down upper 
RelOptInfo. Or, at least, describe in comments why this is desirable 
behaviour. It would be profitable, at least, for extension developers.

I also support the second patch. With many partitions, it allows us to 
save a significant amount of CPU cycles.

-- 
regards, Andrei Lepikhov,
pgEdge