Re: performance regression in 9.2 CTE with SRF function

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: performance regression in 9.2 CTE with SRF function
Date: 2013-02-11 14:36:08
Message-ID: 18987.1360593368@sss.pgh.pa.us
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Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> no, there is strange estimation
>>
>> SubPlan 2
>> -> CTE Scan on pl pl_1 (cost=0.00..468.59
>> rows=89000 width=4) (actual time=0.023..8.379 rows=566 loops=1000)
>> Output: foo(pl_1.a)

Nothing strange about it. 89 rows out from the underlying CTE (which
appears to be dead accurate) times 1000 for the SRF's expansion.

> respective why estimation is unstrable

It isn't --- you are looking at two different subplans there, one with
a SRF in it and one without.

regards, tom lane

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