Re: Possible problem in Custom Scan API

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 = build_path_tlist(root, &best_path->path);
...

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

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