| From: | Donald Dong <xdong(at)csumb(dot)edu> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Different row estimations on base rels |
| Date: | 2019-05-29 20:43:56 |
| Message-ID: | 3A202828-0FEF-4A27-994D-364B15B692F0@csumb.edu |
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| Lists: | pgsql-hackers |
On May 29, 2019, at 1:36 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Well, it's all there in the code. I believe the issue is that the
> final estimates are based on the number of rows that will be returned
> from the relation, which is often less, and occasionally more, than
> the total of the rows in the relation. The reason it's often less is
> because there might be a WHERE clause or similar which rules out some
> of the rows. The reason it might be more is because a nested loop
> could return the same rows multiple times.
Yes, indeed. I was confused, and I guess I could've thought about it
about more before posting here. Thank you for answering this
question!
Regards,
Donald Dong
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