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Subject: Re: Injection points: some tools to wait and wake
From: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
In-Reply-To: <ZdLuxBk5hGpol91B@paquier.xyz>
Date: Mon, 19 Feb 2024 11:54:20 +0300
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>,
 Ashutosh Bapat <ashutosh.bapat@gmail.com>
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Message-Id: <59A65AD3-B392-447A-AF12-2073F63F23A7@yandex-team.ru>
References: <ZdLuxBk5hGpol91B@paquier.xyz>
To: Michael Paquier <michael@paquier.xyz>
Archived-At: <https://www.postgresql.org/message-id/59A65AD3-B392-447A-AF12-2073F63F23A7%40yandex-team.ru>
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> On 19 Feb 2024, at 09:01, Michael Paquier <michael@paquier.xyz> wrote:
>=20
> Thoughts and comments are welcome.

Hi Michael,

thanks for your work on injection points! I want to test a bunch of =
stuff using this facility.

I have a wishlist of functionality that I'd like to see in injection =
points. I hope you will find some of these ideas useful to improve the =
feature.
1. injection_points_wake() will wake all of waiters. But it's not =
suitable for complex tests. I think there must be a way to wake only =
specific waiter by injection point name.
2. Alexander Korotkov's stopevents could be used in isolation tests. =
This kind of tests is perfect for describing complex race conditions. =
(as a side note, I'd be happy if we could have primary\standby in =
isolation tests too)
3. Can we have some Perl function for this?
+# Wait until the checkpointer is in the middle of the restart point
+# processing, relying on the custom wait event generated in the
+# wait callback used in the injection point previously attached.
+ok( $node_standby->poll_query_until(
+		'postgres',
+		qq[SELECT count(*) FROM pg_stat_activity
+           WHERE backend_type =3D 'checkpointer' AND wait_event =3D =
'injection_wait' ;],
+		'1'),
+	'checkpointer is waiting in restart point'
+) or die "Timed out while waiting for checkpointer to run restart =
point";

Perhaps something like
=
$node->do_a_query_and_wait_for_injection_point_observed(sql,injection_poin=
t_name);
4. Maybe I missed it, but I'd like to see a guideline on how to name =
injection points.
5. In many cases we need to have injection point under critical section. =
I propose to have a "prepared injection point". See [0] for example in =
v2-0003-Test-multixact-CV-sleep.patch
+   INJECTION_POINT_PREPARE("GetNewMultiXactId-done");
+
    START_CRIT_SECTION();
=20
+   INJECTION_POINT_RUN_PREPARED();
6. Currently our codebase have files injection_point.c and =
injection_points.c. It's very difficult to remember which is where...
7. This is extremely distant, but some DBMSs allow to enable injection =
points by placing files on the filesystem. That would allow to test =
something during recovery when no SQL interface is present.

Let's test all the neat stuff! Thank you!


Best regards, Andrey Borodin.

[0] =
https://www.postgresql.org/message-id/0925F9A9-4D53-4B27-A87E-3D83A757B0E0=
@yandex-team.ru=