| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | bucoo <bucoo(at)sohu(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: partition wise aggregate wrong rows cost |
| Date: | 2022-05-24 04:16:25 |
| Message-ID: | 1418325.1653365785@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> On Tue, 24 May 2022 at 15:38, bucoo <bucoo(at)sohu(dot)com> wrote:
>> Normal aggregate and partition wise aggregate have a big difference rows cost:
> I wouldn't say this is a bug. Could you not say that they're both
> wrong given that your tables are empty?
We try fairly hard to ensure that the rowcount estimate for a given
relation does not vary across paths, so I concur with the OP that
this is a bug. Having said that, I'm not sure that the consequences
are significant. As you say, the estimates seem to get a lot closer
as soon as the table has some statistics. (But nonetheless, they
are not identical, so it's still a bug.)
regards, tom lane
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