Date: Wed, 12 Jun 2024 10:54:52 -0700
From: Noah Misch <noah@leadboat.com>
To: Robert Haas <robertmhaas@gmail.com>,
	Michael Paquier <michael@paquier.xyz>
Cc: pgsql-hackers@postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>,
	Smolkin Grigory <smallkeen@gmail.com>
Subject: Re: race condition in pg_class
Message-ID: <20240612175452.de.nmisch@google.com>
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On Tue, Jun 11, 2024 at 01:37:21PM +0900, Michael Paquier wrote:
> On Mon, Jun 10, 2024 at 07:19:27PM -0700, Noah Misch wrote:
> > On Fri, Jun 07, 2024 at 09:08:03AM -0400, Robert Haas wrote:
> >> I think the core code should provide an "Injection Point" wait event
> >> type and let extensions add specific wait events there, just like you
> >> did for "Extension".
> > 
> > Michael, could you accept the core code offering that, or not?  If so, I am
> > content to implement that.  If not, for injection point wait events, I have
> > just one priority.  The isolation tester already detects lmgr locks without
> > the test writer teaching it about each lock individually.  I want it to have
> > that same capability for injection points. Do you think we can find something
> > everyone can accept, having that property?  These wait events show up in tests
> > only, and I'm happy to make the cosmetics be anything compatible with that
> > detection ability.
> 
> Adding a wait event class for injection point is an interesting
> suggestion that would simplify the detection in the isolation function
> quite a bit.  Are you sure that this is something that would be fit
> for v17 material?  TBH, I am not sure.

If I were making a list of changes always welcome post-beta, it wouldn't
include adding wait event types.  But I don't hesitate to add one if it
unblocks a necessary test for a bug present in all versions.

> At the end, the test coverage has the highest priority and the bugs
> you are addressing are complex enough that isolation tests of this
> level are a necessity, so I don't object to what
> inplace050-tests-inj-v2.patch introduces with the naming dependency
> for the time being on HEAD.  I'll just adapt and live with that
> depending on what I deal with, while trying to improve HEAD later on.

Here's what I'm reading for each person's willingness to tolerate each option:

STRATEGY                        | Paquier | Misch | Haas
--------------------------------------------------------
new "Injection Point" wait type | maybe   | yes   | yes
INJECTION_POINT(...) naming     | yes     | yes   | unknown
isolation spec says event names | yes     | no    | unknown

Corrections and additional strategy lines welcome.  Robert, how do you judge
the lines where I've listed you as "unknown"?

> I'm still wondering if there is something that could be more elegant
> than a dedicated class for injection points, but I cannot think about
> something that would be better for isolation tests on top of my head.
> If there is something I can think of, I'll just go and implement it :)

I once considered changing them to use advisory lock waits instead of
ConditionVariableSleep(), but I recall that was worse from the perspective of
injection points in critical sections.