| From: | Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> |
|---|---|
| To: | exclusion(at)gmail(dot)com, PostgreSQL mailing lists <pgsql-bugs(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: BUG #16807: Assert failed in postgres_fdw/estimate_path_cost_size with an empty foreign table |
| Date: | 2021-01-14 02:56:08 |
| Message-ID: | CAPmGK16Te7mLsxJ6yaPmJy_qFdmXEmqegxXm4sNQRprYsxtmfg@mail.gmail.com |
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| Lists: | pgsql-bugs |
On Wed, Jan 6, 2021 at 12:15 PM Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> wrote:
> Reproduced. Will look into this closely.
If foreignrel->tuples is set to zero, the retrieved_rows estimate will
also be set to zero, so the assertion pointed out upthread is not
correct. I think I mistakenly assumed that foreignrel->tuples would
have been forced to be at least one row, like foreignrel->rows, before
we get to estimate_path_cost_size(), which is not correct.
To fix, I think it would be better to adjust the assertion accordingly
than removing it, since it was added to make sure that the
retrieved_rows estimate is set to a sensible value. Attached is a
patch for that. I added a simpler test case as well.
Best regards,
Etsuro Fujita
| Attachment | Content-Type | Size |
|---|---|---|
| fix-postgres_fdw-assertion.patch | application/octet-stream | 3.1 KB |
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