[pgpool-hackers: 3951] Re: Patch: Fix flushing of nodata messages for describe statement

[Daniël van de Giessen]

> Attached patch

Hm. It appears my e-mail client on macOS decided this patch wasn't
plain text and set the wrong MIME type, so the attachment was
scrubbed. Let me try this one more time from another OS. :)

Original attachment is also available in the archives at
https://www.pgpool.net/pipermail/pgpool-hackers/attachments/20210709/c0fc0d81/attachment.obj

Best regards,

Daniël van de Giessen
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From c8d7214741b6fbe385e925cb2e1c6036d737d384 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20van=20de=20Giessen?= <daniel at dvdgiessen.nl>
Date: Thu, 8 Jul 2021 23:54:08 +0200
Subject: [PATCH] Fix hang when describing nodata statement

743a69b addressed an hang caused by SimpleForwardToFrontend buffering
the response to a Describe (statement) message by flushing the buffer
for RowDescription messages. However, a NoData message is also a valid
response to certain Describe messages, for example for a "LISTEN"
statement. To fix this we also now flush for a NoData message.
---
 src/protocol/pool_process_query.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/protocol/pool_process_query.c b/src/protocol/pool_process_query.c
index 68db8819..9a2ca8b3 100644
--- a/src/protocol/pool_process_query.c
+++ b/src/protocol/pool_process_query.c
@@ -768,8 +768,8 @@ SimpleForwardToFrontend(char kind, POOL_CONNECTION * frontend,
 
 	/*
 	 * Optimization for other than "Command Complete", "Ready For query",
-	 * "Error response" ,"Notice message", "Notification response" and
-	 * "Row description"
+	 * "Error response" ,"Notice message", "Notification response",
+	 * "Row description" and "No data"
 	 * messages.  Especially, since it is too often to receive and forward
 	 * "Data Row" message, we do not flush the message to frontend now. We
 	 * expect that "Command Complete" message (or "Error response" or "Notice
@@ -780,7 +780,7 @@ SimpleForwardToFrontend(char kind, POOL_CONNECTION * frontend,
 	 * CopyData messages are sent to frontend (typical use case is pg_dump).
 	 * So eliminating per CopyData flush significantly enhances performance.
 	 */
-	if (kind == 'C' || kind == 'Z' || kind == 'E' || kind == 'N' || kind == 'A' || kind == 'T')
+	if (kind == 'C' || kind == 'Z' || kind == 'E' || kind == 'N' || kind == 'A' || kind == 'T' || kind == 'n')
 	{
 		pool_write_and_flush(frontend, p1, len1);
 	}
-- 
2.25.1