Re: Order by (for 15 rows) adds 30 seconds to query time - Mailing list pgsql-performance

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

> And yeah, I think the statistical support is pretty crummy.

Do you know, off-hand, why the estimated row count for a "Nested
Loop Left Join" is not the product of the estimates for the two
sides?  (I fear I'm missing something important which lead to the
current estimates.)

Estimates extracted from the problem plan:

  Nested Loop Left Join  (rows=806903677108)
    ->  Nested Loop Left Join  (rows=203176856)
          ->  Nested Loop Left Join  (rows=51160)
                ->  Nested Loop Left Join  (rows=28)
                ->  Append  (rows=4)
          ->  Append  (rows=2)
    ->  Append  (rows=2)

-Kevin