Re: Very ineffective plan with merge join

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
Cc: "Pgsql Hackers" <pgsql-hackers@postgresql.org>, "Oleg Bartunov" <oleg@sai.msu.su>
Date: 2010-04-15T22:00:58Z
Lists: pgsql-hackers
"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> What's up with the sort of _accrged7200 (in the slower plan) taking
> in 3.5 million rows and putting out 1 row?  There's something there
> I'm not understanding.

It's under a merge join, so what probably happened is that the first
row from that side had a larger key than any row from the other side.
A mergejoin will never bother to look at the remaining rows in such
a case.

			regards, tom lane