| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Wrong results from Parallel Hash Full Join |
| Date: | 2023-06-12 03:24:24 |
| Message-ID: | ZIaP6ODzLVGa/waB@paquier.xyz |
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| Lists: | pgsql-hackers |
On Wed, Jun 07, 2023 at 05:16:12PM -0400, Melanie Plageman wrote:
> On Fri, May 19, 2023 at 8:05 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Considering that this is a parallel plan, I don't think there's any
>> mystery about why an ORDER-BY-less query might have unstable output
>> order; the only mystery is why more of the buildfarm hasn't failed.
>> Can we just add "ORDER BY t1.id" to this query? It looks like you
>> get the same PHJ plan, although now underneath Sort/Gather Merge.
>
> Yes, this was an oversight on my part. Attached is the patch that does
> just what you suggested.
Confirmed that adding an ORDER BY adds a Sort node between a Gather
Merge and a Parallel Hash Full Join, not removing coverage.
This has fallen through the cracks and conchuela has failed again
today, so I went ahead and applied the fix on HEAD. Thanks!
--
Michael
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