Received-SPF: SoftFail (my.malkut.net: domain of malkut.net does not designate
 89.247.174.62 as permitted sender) receiver=my.malkut.net; identity=mailfrom;
 client-ip=89.247.174.62 helo=[192.168.7.153];
 envelope-from=<arne.roland@malkut.net>
Message-ID: <542c1950-2bea-4fc2-911c-b18c0ec5d62b@malkut.net>
Date: Thu, 18 Jan 2024 07:39:09 +0100
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: A performance issue with Memoize
Content-Language: en-US
To: Richard Guo <guofenglinux@gmail.com>,
 Andrei Lepikhov <a.lepikhov@postgrespro.ru>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
References: 
 <CAMbWs48XHJEK1Q1CzAQ7L9sTANTs9W1cepXu8=Kc0quUL+tg4Q@mail.gmail.com>
 <1d55df6d-92cb-4bbd-9a4c-0d05bb6bc91d@postgrespro.ru>
 <CAMbWs49qgcP2syquh=Ep4LEn4Kyu_Y+dd48pDhfFg0Cwq1y0UQ@mail.gmail.com>
 <dd90a086-c860-49f3-9e71-ac987e5ac522@postgrespro.ru>
 <CAMbWs4-OmOT0nnAKSQ8ydeu_ZvxYcjfzQS9GEuyOXpPaqqQwXg@mail.gmail.com>
From: Arne Roland <arne.roland@malkut.net>
In-Reply-To: 
 <CAMbWs4-OmOT0nnAKSQ8ydeu_ZvxYcjfzQS9GEuyOXpPaqqQwXg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: 
 <https://www.postgresql.org/message-id/542c1950-2bea-4fc2-911c-b18c0ec5d62b%40malkut.net>
Precedence: bulk

Hi Richard,

I can tell this a real world problem. I have seen this multiple times in 
production.

The fix seems surprisingly simple.

I hope my questions here aren't completely off. I still struggle to 
think about the implications.

I wonder, if there is any stuff we are breaking by bluntly forgetting 
about the subplan params. Maybe some table valued function scan within a 
subquery scan? Or something about casts on a join condition, that could 
be performed differently?

I wasn't able to construct a problem case. I might be just missing 
context here. But I am not yet fully convinced whether this is safe to 
do in all cases.

Regards
Arne