Re: [HACKERS] Removing [Merge]Append nodes which contain a single subpath

On Thu, Mar 15, 2018 at 11:01 AM, Tom Lane <tgl@sss.pgh.pa.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