From: "Carlo Stonebanks" <stonec.register@sympatico.ca>
Subject: REPOST: Nested loops row estimates always too high
Date: Thu, 20 Sep 2007 11:02:55 -0400
Organization: Hub.Org Networking Services
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Message-ID: <fcu215$2em3$1@news.hub.org>
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To: pgsql-performance@postgresql.org

(SORRY FOR THE REPOST, I DON'T SEE MY ORIGINAL QUESTION OR ANY ANSWERS HERE)

I am noticing that my queries are spending a lot of time in nested loops. 
The table/index row estimates are not bad, but the nested loops can be off 
by a factor of 50. In any case, they are always too high.

Are the over-estimations below significant, and if so, is this an indication 
of a general configuration problem?

Carlo


select
   pp.provider_id,
   pp.provider_practice_id,
   nearby.distance
from mdx_core.provider_practice as pp
join mdx_core.facility as f
on f.facility_id = pp.facility_id
join (select * from mdx_core.zips_in_mile_range('08820', 10) where zip > '') 
as nearby
on f.default_country_code = 'US'
   and f.default_postal_code = nearby.zip
   and pp.facility_address_id is NULL
union select
   pp.provider_id,
   pp.provider_practice_id,
   nearby.distance
from mdx_core.provider_practice as pp
join mdx_core.facility_address as fa
on fa.facility_address_id = pp.facility_address_id
join mdx_core.address as a
on a.address_id = fa.address_id
join (select * from mdx_core.zips_in_mile_range('08820', 10) where zip > '') 
as nearby
on a.country_code = 'US'
and a.postal_code = nearby.zip

Unique  (cost=67605.91..67653.18 rows=4727 width=16) (actual 
time=8634.618..8637.918 rows=907 loops=1)
  ->  Sort  (cost=67605.91..67617.73 rows=4727 width=16) (actual 
time=8634.615..8635.651 rows=907 loops=1)
        Sort Key: provider_id, provider_practice_id, distance
        ->  Append  (cost=0.00..67317.41 rows=4727 width=16) (actual 
time=176.056..8632.429 rows=907 loops=1)
              ->  Nested Loop  (cost=0.00..38947.07 rows=3143 width=16) 
(actual time=176.054..7867.962 rows=872 loops=1)
                    ->  Nested Loop  (cost=0.00..11520.79 rows=8121 
width=12) (actual time=169.372..3041.010 rows=907 loops=1)
                          ->  Function Scan on zips_in_mile_range 
(cost=0.00..15.00 rows=333 width=40) (actual time=151.479..151.671 rows=66 
loops=1)
                                Filter: (zip > ''::text)
                          ->  Index Scan using 
facility_country_postal_code_idx on facility f  (cost=0.00..34.25 rows=24 
width=15) (actual time=4.969..43.740 rows=14 loops=66)
                                Index Cond: ((f.default_country_code = 
'US'::bpchar) AND ((f.default_postal_code)::text = zips_in_mile_range.zip))
                    ->  Index Scan using provider_practice_facility_idx on 
provider_practice pp  (cost=0.00..3.36 rows=1 width=12) (actual 
time=4.915..5.316 rows=1 loops=907)
                          Index Cond: (f.facility_id = pp.facility_id)
                          Filter: (facility_address_id IS NULL)
              ->  Nested Loop  (cost=0.00..28323.07 rows=1584 width=16) 
(actual time=170.310..762.472 rows=35 loops=1)
                    ->  Nested Loop  (cost=0.00..7791.77 rows=1579 width=12) 
(actual time=170.289..612.579 rows=36 loops=1)
                          ->  Nested Loop  (cost=0.00..2595.96 rows=712 
width=12) (actual time=167.017..354.261 rows=29 loops=1)
                                ->  Function Scan on zips_in_mile_range 
(cost=0.00..15.00 rows=333 width=40) (actual time=150.188..150.312 rows=66 
loops=1)
                                      Filter: (zip > ''::text)
                                ->  Index Scan using 
address_country_postal_code_address_idx on address a  (cost=0.00..7.73 
rows=2 width=17) (actual time=2.483..3.086 rows=0 loops=66)
                                      Index Cond: ((a.country_code = 
'US'::bpchar) AND ((a.postal_code)::text = zips_in_mile_range.zip))
                          ->  Index Scan using facility_address_address_idx 
on facility_address fa  (cost=0.00..7.15 rows=12 width=8) (actual 
time=7.652..8.901 rows=1 loops=29)
                                Index Cond: (a.address_id = fa.address_id)
                    ->  Index Scan using 
provider_practice_facility_address_idx on provider_practice pp 
(cost=0.00..12.80 rows=16 width=12) (actual time=4.156..4.158 rows=1 
loops=36)
                          Index Cond: (fa.facility_address_id = 
pp.facility_address_id)
Total runtime: 8639.066 ms