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Message-ID: <8d65f84d-ddb3-4d0f-be05-44f443500e41@aklaver.com>
Date: Mon, 13 Jan 2025 09:26:09 -0800
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Subject: Re: Intermittent errors when fetching cursor rows on PostgreSQL 16
To: Enrico Schenone <eschenone@cleistech.it>,
 pgsql-general@lists.postgresql.org
Cc: Massimo Catti <mcatti@cleistech.it>, Livio Pizzolo <lpizzolo@cleistech.it>
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From: Adrian Klaver <adrian.klaver@aklaver.com>
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On 1/13/25 08:59, Enrico Schenone wrote:
> 
> Il 13/01/25 17:19, Adrian Klaver ha scritto:
>> On 1/13/25 00:45, Enrico Schenone wrote:
>>> Hello, Adrian.
>>> As I said days ago, I have arranged a kind of stress test in 
>>> production environment.
>>> I wrote a program that loads a temporary table, loads 2049 rows into 
>>> them from a baseline_table and finally declare two nested cursors.
>>> The first cursor is on the temp table as parent while the second is 
>>> on a lookup table as child.
>>>
>>> The program logic is the transposition of one fragment of several 
>>> production programs that was failing on cursors, and has to be 
>>> intended as a POC only.
>>>
>>
>>
>>> And Well, I'm quite confused: no error at all has been detected, not 
>>> only on the test programs but in the whole production system. The 
>>> error was completely disappeared.
>>>
>>> Then I have stopped the four tasks of the stress test leaving all 
>>> other services running for a week, and again no error at all.
>>>
>>> No setup was changed nor servers was rebooted, nor infrastructure has 
>>> been upgraded during the test period.
>>
>> You are absolutely sure about the above?
> I can say Yes. All test operations has been logged and verified against 
> the Postgresql log.
> The only component not under my control is the Provider's 
> Infrastructure, but  the infrastructure admin ensured me that no 
> operation at all has been made. I beleave him because it is a reliable 
> tecnician end a well known person.

In your OP you stated:

"Production environments can be:

  * Distinct application server and DB server on distinct subnets (no
     dropped packet detected on firewall, no memory/disk/network failure
     detected by "nmon" tool)
   * Distinct application server and DB server on same subnet (no firewall)
   * Same server for PostgreSQL and applications
"

In all those cases are the various servers all running completely within 
the providers infrastructure?


>> Errors that 'fix' themselves are the most frustrating kind, as you 
>> know in the back of your mind they will likely pop up again.
> True, knocking again to my door ... I still can't beleave.

Going forward one of three things are likely to happen:

1) The error never shows again.

2) It does show up again but in a manner that allows it to be traced.

3) The worst case, it plays hide and seek as previously.


> Thanks a lot for your interest in sharing my strange experience.
> Best regards.
> Enrico
> 
> *Enrico Schenone*
> Software Architect

-- 
Adrian Klaver
adrian.klaver@aklaver.com