From: | Donald Dong <xdong(at)csumb(dot)edu> |
---|---|
To: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | How does the planner determine plan_rows ? |
Date: | 2019-01-11 02:41:46 |
Message-ID: | 9BFB8B01-6E2B-4F65-A9B5-299BCB69A1C0@csumb.edu |
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Hi,
I created some empty tables and run ` EXPLAIN ANALYZE` on `SELECT * `. I found
the results have different row numbers, but the tables are all empty.
=# CREATE TABLE t1(id INT, data INT);
=# EXPLAIN ANALYZE SELECT * FROM t1;
Seq Scan on t1 (cost=0.00..32.60 rows=2260 width=8) (actual
time=0.003..0.003 rows=0 loops=1)
=# CREATE TABLE t2(data VARCHAR);
=# EXPLAIN ANALYZE SELECT * FROM t2;
Seq Scan on t2 (cost=0.00..23.60 rows=1360 width=32) (actual
time=0.002..0.002 rows=0 loops=1)
=# CREATE TABLE t3(id INT, data VARCHAR);
=# EXPLAIN ANALYZE SELECT * FROM t3;
Seq Scan on t3 (cost=0.00..22.70 rows=1270 width=36) (actual
time=0.001..0.001 rows=0 loops=1)
I found this behavior unexpected. I'm still trying to find out how/where the planner
determines the plan_rows. Any help will be appreciated!
Thank you,
Donald Dong
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