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Re: pgbench: make verbose error messages thread-safe

Alex Guo <guo.alex.hengchen@gmail.com>

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From: Alex Guo <guo.alex.hengchen@gmail.com>
To: Fujii Masao <masao.fujii@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-24T08:09:06Z
Lists: pgsql-hackers 
On 4/24/26 2:26 PM, Fujii Masao wrote:
> 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,
>
In single-threaded mode, reusing the static local buffer might be 
slightly more performant. But if this function needs to be safe in 
multi-threaded mode, then we have to stop using a static local variable.

So the change looks reasonable and good to me.

Regards,
Alex Guo

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  1. pgbench: fix verbose error message corruption with multiple threads