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From: Max Ulidtko <[email protected]>
To: [email protected]
Subject: Getting error 42P02, despite query parameter being sent
Date: Sat, 16 Nov 2024 11:55:35 +0100
Message-ID: <[email protected]> (raw)

Greetings, group!

I'm trying to understand a low-level issue. Am evaluating a new client 
library for Postgres; it's not particularly popular / mainstream, and 
as I've understood so far, sports an independent implementation of PG 
binary protocol.

The issue I'm hitting with it is exemplified by server logs like this:

2024-11-16 10:28:19.927 UTC [46] LOG: statement: SET client_encoding = 
'UTF8';SET client_min_messages TO WARNING;
2024-11-16 10:28:19.928 UTC [46] LOG: execute <unnamed>: CREATE VIEW 
public.foobar (alg, hash) AS VALUES ('md5', $1);
2024-11-16 10:28:19.928 UTC [46] DETAIL: parameters: $1 = 
'test-param-value'
2024-11-16 10:28:19.928 UTC [46] ERROR: there is no parameter $1 at 
character 57

Of course, I /am/ passing a value for parameter $1; and I can trace 
that the client lib sends it out on the wire as expected. (Attaching 
packet captures.)

Heck, even the PG server itself says, DETAIL: parameters: $1 = 
'test-param-value' — so it sees the parameter! But then, immediately 
unsees it.

Am I being hit by a PG bug? Is this a known issue?

I'd retested with master version of that client library, and against 6 
latest major versions of PostgreSQL server (12 throughout to 17). No 
difference across versions spotted; the result is consistently error 
42P02.

Is the client library doing something wrong? How can the server claim 
there's no parameter $1 immediately after logging its value it has 
received?

I did minify a 100-line SSCCE that reproduces the issue and can be 
shared.

Any advice, or pointers on what to check next besides delving into PG 
source, I'd greatly appreciate. Thanks in advance.

Max




Attachments:

  [application/vnd.tcpdump.pcap] query42P02-with-prepstatement-on.pcap (2.5K, 3-query42P02-with-prepstatement-on.pcap)
  download

  [application/vnd.tcpdump.pcap] query42P02-with-prepstatement-off.pcap (2.3K, 4-query42P02-with-prepstatement-off.pcap)
  download

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