[Ning Sun <classicning@gmail.com>]

Hi,

I'm maintaining a Rust library pgwire to implement postgres wire 
protocol in rust. While doing a corner case test, I noticed the 
inconsistency for ParameterDescription between backend and frontend.

The backend allows up to 65535 parameters in a prepared statement. But 
when running Describe on the statement, there is a size limit of 30000 
bytes for ParameterDescription on the frontend. This means we can only 
describe statements with at most ~7500 parameters. For statements exceed 
the limit, it ends up with error about the message size.

This patch simply adds ParameterDescription to VALID_LONG_MESSAGE_TYPE 
whitelist to remove the cap.

Attachments:

0001-add-ParameterDescription-to-long-message-types.patch (text/x-patch, 829B) download
From 6036564be819db0beb3efc1ad52c981922d52529 Mon Sep 17 00:00:00 2001
From: Ning Sun <sunning@greptime.com>
Date: Wed, 1 Apr 2026 11:53:38 +0800
Subject: [PATCH] add ParameterDescription to long message types

---
 src/interfaces/libpq/fe-protocol3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 8c1fda5caf0..7fd49cb151e 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -42,7 +42,8 @@
 	 (id) == PqMsg_FunctionCallResponse || \
 	 (id) == PqMsg_NoticeResponse || \
 	 (id) == PqMsg_NotificationResponse || \
-	 (id) == PqMsg_RowDescription)
+	 (id) == PqMsg_RowDescription || \
+	 (id) == PqMsg_ParameterDescription)
 
 
 static void handleFatalError(PGconn *conn);
-- 
2.53.0