From: Chao Li <li.evan.chao@gmail.com>
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Subject: pg_test_timing: fix unit typo and widen diff type
Message-Id: <F780CEEB-A237-4302-9F55-60E9D8B6533D@gmail.com>
Date: Thu, 2 Apr 2026 11:09:23 +0800
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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Hi,

This morning, as part of my usual routine, I synced the master branch =
and read through the recent commits. While reading 82c0cb4e672, I =
noticed a mistake in an error message. The relevant code is like:
```
diff =3D INSTR_TIME_GET_NANOSEC(diff_time);

fprintf(stderr, _("Time warp: %d ms\n"), diff);
```

Here, =E2=80=9Cdiff" is in nanoseconds, but the error message prints ms =
as the unit, which is incorrect.

To fix that, I think there are two possible options:

1. Use INSTR_TIME_GET_MILLISEC to get =E2=80=9Cdiff"
2. Change =E2=80=9Cms" to =E2=80=9Cns" in the error message

After reading through the whole file, I think option 2 is the right fix. =
While doing that, I also noticed another issue.

=E2=80=9Cdiff" is currently defined as int32. Although one might think =
that is enough for a time delta, I believe it should be int64 for two =
reasons:

* INSTR_TIME_GET_NANOSEC() explicitly returns int64:
```
#define INSTR_TIME_GET_NANOSEC(t) \
               ((int64) (t).ticks)
```

* The current code has a sanity check for backward clock drift:
```
        /* Did time go backwards? */
        if (unlikely(diff < 0))
        {
            fprintf(stderr, _("Detected clock going backwards in =
time.\n"));
            fprintf(stderr, _("Time warp: %d ms\n"), diff);
            exit(1);
        }
```
Clock jumping forward is also possible, and a forward jump of about 2.14 =
seconds would overflow int32 when expressed in nanoseconds, making the =
value appear negative. In that case, the code could report a =
=E2=80=9Cbackwards=E2=80=9D clock jump when the actual jump was =
forwards, which would be misleading.

To make the patch easier to process, I split it into two parts: 0001 =
fixes the unit in the error message, and 0002 changes the type of diff. =
If this gets accepted, I would be happy to squash them into one commit.

I should also note that although I noticed this while reading =
82c0cb4e672, I do not think this was an oversight of that commit. More =
likely, because clock drift backwards is rare, this issue has simply =
gone unnoticed for many years.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/


--Apple-Mail=_5D6B312F-5340-4C15-82F5-67111BAF2BE0
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--Apple-Mail=_5D6B312F-5340-4C15-82F5-67111BAF2BE0
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