Hi, While running pgbench with multiple threads and --verbose-errors, I found that some verbose error messages were corrupted. This issue happens because printVerboseErrorMessages() uses a function-local static PQExpBuffer for building those messages. Since that buffer is shared across threads, it is not thread-safe.
Attached patch fixes this issue by changing printVerboseErrorMessages() to use a local PQExpBufferData instead of a static one. Thoughts? Since this issue was introduced in v15, the patch should be backpatched to v15 if accepted. Regards, -- Fujii Masao
From f1056e0793812118c462a2338ff2ca5ab5ce55ce Mon Sep 17 00:00:00 2001 From: Fujii Masao <[email protected]> Date: Fri, 24 Apr 2026 14:50:48 +0900 Subject: [PATCH v1] 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. --- src/bin/pgbench/pgbench.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c index 80d14108c28..dc0c48f86f0 100644 --- a/src/bin/pgbench/pgbench.c +++ b/src/bin/pgbench/pgbench.c @@ -3586,23 +3586,20 @@ 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); - appendPQExpBuffer(buf, "%s", + printfPQExpBuffer(&buf, "client %d ", st->id); + appendPQExpBuffer(&buf, "%s", (is_retry ? "repeats the transaction after the error" : "ends the failed transaction")); - appendPQExpBuffer(buf, " (try %u", st->tries); + appendPQExpBuffer(&buf, " (try %u", st->tries); /* Print max_tries if it is not unlimitted. */ 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 @@ -3611,12 +3608,14 @@ 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)); } - appendPQExpBuffer(buf, ")\n"); + appendPQExpBuffer(&buf, ")\n"); - pg_log_info("%s", buf->data); + pg_log_info("%s", buf.data); + + termPQExpBuffer(&buf); } /* -- 2.53.0
v1-0001-pgbench-fix-verbose-error-message-corruption-with.patch
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