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Subject: Re: [Proposal] Adding callback support for custom statistics kinds
From: Chao Li <li.evan.chao@gmail.com>
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Date: Tue, 9 Dec 2025 11:38:53 +0800
Cc: Michael Paquier <michael@paquier.xyz>,
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To: Sami Imseih <samimseih@gmail.com>
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> On Dec 9, 2025, at 03:09, Sami Imseih <samimseih@gmail.com> wrote:
>=20
>> Yes, thanks.  Structurally, this is better and more flexible than =
what
>> we had originally, and I have noticed that you have copied the
>> original files while adding more comments and renaming a bit things:
>> the structure of the functions was exactly the same.  Anyway, I have
>> worked on that for a good portion of the day, splitting the module
>> drop and the new module into two commits, and applied the result =
after
>> tweaking quite a few things in terms of names and comments (no
>> pgstat_*, a bit more "Var" and "Fixed", etc.), applying a much more
>> consistent set of names across the board for the functions and the
>> structures.  This cleanup part is moved out of the way now, so that
>> you ease the introduction of the next pieces you are proposing.
>=20
> Thanks for getting these committed!
>=20
> I rebased the custom callbacks patch in v5.
>=20
> One very minor thing from the earlier commits that I corrected here is
> the test for entry 2 after a clean restart.
>=20
> -is($result, "entry1|2", "variable-sized stats persist after clean =
restart");
> +is($result, "entry1|2|Test entry 1", "variable-sized stats persist
> after clean restart");
> +
> +$result =3D $node->safe_psql('postgres', q(select * from
> test_custom_stats_var_report('entry2')));
> +is($result, "entry2|3|Test entry 2", "variable-sized stats persist
> after clean restart");
> +
>=20
> --
> Sami Imseih
> Amazon Web Services (AWS)
> <v5-0001-Allow-cumulative-statistics-to-serialize-auxiliar.patch>

```
+					if =
(kind_info->from_serialized_extra_stats)
+					{
+						if =
(!kind_info->from_serialized_extra_stats(&key, header, fpin))
+						{
+							elog(WARNING, =
"could not read extra stats for entry %u/%u/%" PRIu64,
+								 =
key.kind, key.dboid, key.objid);
+							goto error;
+						}
+					}
```

When deserialize failed, it goes to error. In the error clause, it calls =
pgstat_reset_after_failure(), so do we want to give extensions a chance =
to do some reset operations? If yes, then we can add a =
reset_after_failure() callback.

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