Re: nested loop semijoin estimates

On 05/30/15 21:50, Tom Lane wrote:
> So what this seems to mean is that for SEMI/ANTI join cases, we have
> to postpone all of the inner scan cost determination to
> final_cost_nestloop, so that we can do this differently depending on
> whether has_indexed_join_quals() is true. That's a little bit
> annoying because it will mean we take the shortcut exit less often;
> but since SEMI/ANTI joins aren't that common, it's probably not
> going to be a big planning time hit.

Yay! So I wasn't entirely wrong on this. Do you plan to make this 
change, or will you leave that on me?

>
> Not sure yet about your other point about the indexscan getting
> rejected too soon. That doesn't seem to be happening for me, at least
> not in HEAD.

FWIW I can reproduce that reliably on current HEAD, with the test case I 
sent yesterday. I'm using default config (as produced by initdb).

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services