From: | Donald Dong <xdong(at)csumb(dot)edu> |
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To: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Different row estimations on base rels |
Date: | 2019-05-26 17:00:18 |
Message-ID: | C48F353B-A15F-4A69-A49D-38ADA6B8F131@csumb.edu |
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Lists: | pgsql-hackers |
Hi,
I noticed the estimated rows of the base relations during the join
searching is *very* different from the estimations in the final plan.
Join search (rows of the initial_rels):
RELOPTINFO (ct): rows=1 width=4
RELOPTINFO (it): rows=1 width=4
RELOPTINFO (mc): rows=17567 width=32
RELOPTINFO (mi_idx): rows=1380035 width=8
RELOPTINFO (t): rows=2528356 width=25
The final plan:
Seq Scan on company_type ct
(cost=0.00..1.05 rows=1 width=4)
Seq Scan on info_type it
(cost=0.00..2.41 rows=1 width=4)
Parallel Seq Scan on movie_companies mc
(cost=0.00..37814.90 rows=7320 width=32)
Parallel Seq Scan on movie_info_idx mi_idx
(cost=0.00..13685.15 rows=575015 width=8)
Index Scan using title_pkey on title t
(cost=0.43..0.58 rows=1 width=25)
By looking at the joinrel->rows, I would expect relation t to have
the largest size, however, this is not true at all. I wonder what's
causing this observation, and how to get estimations close to the
final plan?
Thank you,
Donald Dong
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