Nikhil Sontakke <nikhil.sontakke@enterprisedb.com> wrote:
> I observed the following behavior on PG head:
> postgres=# explain verbose insert into public.x values (generate_series(1,10));
> ------------------------------------------------
> �Insert �(cost=0.00..0.01 rows=1 width=0)
Hmmm, there are differences between "SELECT SRF()" and "SELECT * FROM SRF()":
postgres=# EXPLAIN INSERT INTO public.x SELECT generate_series(1,10); QUERY PLAN
------------------------------------------------Insert (cost=0.00..0.02 rows=1 width=4) -> Result (cost=0.00..0.01
rows=1width=0)
postgres=# EXPLAIN INSERT INTO public.x SELECT * FROM generate_series(1,10); QUERY PLAN
------------------------------------------------------------------------------Insert (cost=0.00..10.00 rows=1000
width=4) -> Function Scan on generate_series (cost=0.00..10.00 rows=1000 width=4)
> I think the place where we set the
> targetlist of the result_plan to sub_tlist, immediately after that we
> should update the plan_rows estimate by walking this latest
> targetlist. I did that and now we seem to get proper row estimates.
I agree the estimation should be improved, but your patch *adds*
the estimated number of rows to the result:
postgres=# EXPLAIN INSERT INTO public.x SELECT generate_series(1,10); QUERY PLAN
---------------------------------------------------Insert (cost=0.00..12.52 rows=1002 width=4) -> Result
(cost=0.00..2.51rows=1001 width=0)
Should it be 1000 rather than 1001?
Regards,
---
Takahiro Itagaki
NTT Open Source Software Center
