| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Removing [Merge]Append nodes which contain a single subpath |
| Date: | 2018-03-15 15:43:06 |
| Message-ID: | CA+TgmoY3rmSPs15iWxxw3aiOqEcxLi_1nRN0otG6ycPcwYRjMw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Mar 15, 2018 at 11:01 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> It might be worth looking at whether we couldn't fix the single-member-
> Append issue the same way we fix no-op SubqueryScans, ie let setrefs.c
> get rid of them. That's not the most beautiful solution perhaps, but
> it'd be very localized and low-risk.
That's definitely a thought; it's a probably the simplest way of
saving the run-time cost of the Append node. However, I don't think
it's a great solution overall because it doesn't get us the other
advantages that David mentions in his original post. I think that to
gain those advantages we'll need to know at path-creation time that
there won't ultimately be an Append node in the finished plan.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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