From: Tristan Partin <tristan@neon.tech>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-hackers@lists.postgresql.org
Subject: Re: Two small bugs in guc.c
Date: Wed, 27 Dec 2023 12:26:42 -0600
Message-ID: <CXZBTBI4CC14.19ODDAQ7T9KMB@neon.tech> (raw)
In-Reply-To: <2089235.1703617353@sss.pgh.pa.us>
References: <2089235.1703617353@sss.pgh.pa.us>
On Tue Dec 26, 2023 at 1:02 PM CST, Tom Lane wrote:
> I investigated the report at [1] about pg_file_settings not reporting
> invalid values of "log_connections". It turns out it's broken for
> PGC_BACKEND and PGC_SU_BACKEND parameters, but not other ones.
> The cause is a bit of premature optimization in this logic:
>
> * If a PGC_BACKEND or PGC_SU_BACKEND parameter is changed in
> * the config file, we want to accept the new value in the
> * postmaster (whence it will propagate to
> * subsequently-started backends), but ignore it in existing
> * backends. ...
>
> Upon detecting that case, set_config_option just returns -1 immediately
> without bothering to validate the value. It should check for invalid
> input before returning -1, which we can mechanize with a one-line fix:
>
> - return -1;
> + changeVal = false;
>
> While studying this, I also noted that the bit to prevent changes in
> parallel workers seems seriously broken:
>
> if (IsInParallelMode() && changeVal && action != GUC_ACTION_SAVE)
> ereport(elevel,
> (errcode(ERRCODE_INVALID_TRANSACTION_STATE),
> errmsg("cannot set parameters during a parallel operation")));
>
> This is evidently assuming that ereport() won't return, which seems
> like a very dubious assumption given the various values that elevel
> can have. Maybe it's accidentally true -- I don't recall any
> reports of trouble here -- but it sure looks fragile.
>
> Hence, proposed patch attached.
Looks good to me.
--
Tristan Partin
Neon (https://neon.tech)
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To: pgsql-hackers@postgresql.org
Cc: tristan@neon.tech, tgl@sss.pgh.pa.us, pgsql-hackers@lists.postgresql.org
Subject: Re: Two small bugs in guc.c
In-Reply-To: <CXZBTBI4CC14.19ODDAQ7T9KMB@neon.tech>
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