From: Dmitry Ivanov <d.ivanov@postgrespro.ru>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dmitry Ivanov <d.ivanov@postgrespro.ru>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Possible problem in Custom Scan API
Date: Tue, 11 Apr 2017 21:33:15 +0300
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Tom Lane wrote:
> Uh, why would you see that?  The planner would never generate an
> IndexOnlyScan in the first place if the query required any columns
> not available from the index.

True, but as you can see, create_append_plan() produces its own targetlist:

static Plan *
create_append_plan(PlannerInfo *root, AppendPath *best_path)
{
	Append	   *plan;
	List	   *tlist =3D build_path_tlist(root, &best_path->path);
	...

If we replace Append with some custom node, the plan will instantly become=
=20
invalid (it won't be be able to build a projection from 'custom_scan_tlist'=
=20
to 'targetlist'). However, this doesn't mean that it's unable to produce=20
the same result.


--=20
Dmitry Ivanov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company


--=20
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