| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Do CustomScan as not projection capable node |
| Date: | 2019-04-22 18:06:52 |
| Message-ID: | 20250.1555956412@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> writes:
> It is possible that custom_scan_tlist is designed too nontrivially, and
> it is possible that it needs some comments describing in more detail how
> to use it.
I totally buy the argument that the custom scan stuff is
underdocumented :-(.
FWIW, if we did have a use-case showing that somebody would like to make
custom scans that can't project, the way to do it would be to add a flag
bit showing whether a particular CustomPath/CustomScan could project or
not. Not to assume that they all can't. This wouldn't be that much code
really, but I'd still like to see a plausible use-case before adding it,
because it'd be a small API break for existing CustomPath providers.
regards, tom lane
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