From: Fujii Masao <fujii@postgresql.org>
Date: Thu, 14 May 2026 03:30:34 +0000 (+0900)
Subject: pgbench: fix verbose error message corruption with multiple threads
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=61f8a85a577fd0ea0bf924a88064187bed31eb48;p=thirdparty%2Fpostgresql.git

pgbench: fix verbose error message corruption with multiple threads

When pgbench runs with multiple threads and verbose error reporting is
enabled (--verbose-errors), multiple clients can build verbose error
messages concurrently. Previously, a function-local static
PQExpBuffer was used for these messages, causing the buffer to be
shared across threads. This was not thread-safe and could result in
corrupted or incorrect log output.

Fix this by using a local PQExpBufferData instead of a static buffer.
This keeps verbose error messages correct during concurrent execution.

Backpatch to v15, where this issue was introduced.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Alex Guo <guo.alex.hengchen@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwER1AjGXpkKB9t9820NBhMQ_Ghv7=HsKeodUr3=SZsF4g@mail.gmail.com
Backpatch-through: 15
---

diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index 69b12a919a4..0b2bb9340b5 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -3630,22 +3630,19 @@ getTransactionStatus(PGconn *con)
 static void
 printVerboseErrorMessages(CState *st, pg_time_usec_t *now, bool is_retry)
 {
-	static PQExpBuffer buf = NULL;
+	PQExpBufferData buf;
 
-	if (buf == NULL)
-		buf = createPQExpBuffer();
-	else
-		resetPQExpBuffer(buf);
+	initPQExpBuffer(&buf);
 
-	printfPQExpBuffer(buf, "client %d ", st->id);
-	appendPQExpBufferStr(buf, (is_retry ?
-							   "repeats the transaction after the error" :
-							   "ends the failed transaction"));
-	appendPQExpBuffer(buf, " (try %u", st->tries);
+	printfPQExpBuffer(&buf, "client %d ", st->id);
+	appendPQExpBufferStr(&buf, (is_retry ?
+								"repeats the transaction after the error" :
+								"ends the failed transaction"));
+	appendPQExpBuffer(&buf, " (try %u", st->tries);
 
 	/* Print max_tries if it is not unlimited. */
 	if (max_tries)
-		appendPQExpBuffer(buf, "/%u", max_tries);
+		appendPQExpBuffer(&buf, "/%u", max_tries);
 
 	/*
 	 * If the latency limit is used, print a percentage of the current
@@ -3654,12 +3651,14 @@ printVerboseErrorMessages(CState *st, pg_time_usec_t *now, bool is_retry)
 	if (latency_limit)
 	{
 		pg_time_now_lazy(now);
-		appendPQExpBuffer(buf, ", %.3f%% of the maximum time of tries was used",
+		appendPQExpBuffer(&buf, ", %.3f%% of the maximum time of tries was used",
 						  (100.0 * (*now - st->txn_scheduled) / latency_limit));
 	}
-	appendPQExpBufferStr(buf, ")\n");
+	appendPQExpBufferStr(&buf, ")\n");
 
-	pg_log_info("%s", buf->data);
+	pg_log_info("%s", buf.data);
+
+	termPQExpBuffer(&buf);
 }
 
 /*