Re: race condition in pg_class

On Sun, May 12, 2024 at 04:29:23PM -0700, Noah Misch wrote:
> I'm attaching patches implementing the LockTuple() design. It turns out we
> don't just lose inplace updates. We also overwrite unrelated tuples,
> reproduced at inplace.spec. Good starting points are README.tuplock and the
> heap_inplace_update_scan() header comment.

About inplace050-tests-inj-v1.patch.

+ /* Check if blocked_pid is in injection_wait(). */
+ proc = BackendPidGetProc(blocked_pid);
+ if (proc == NULL)
+ PG_RETURN_BOOL(false); /* session gone: definitely unblocked */
+ wait_event =
+ pgstat_get_wait_event(UINT32_ACCESS_ONCE(proc->wait_event_info));
+ if (wait_event && strncmp("INJECTION_POINT(",
+ wait_event,
+ strlen("INJECTION_POINT(")) == 0)
+ PG_RETURN_BOOL(true);

Hmm. I am not sure that this is the right interface for the job
because this is not only related to injection points but to the
monitoring of a one or more wait events when running a permutation
step. Perhaps this is something that should be linked to the spec
files with some property area listing the wait events we're expected
to wait on instead when running a step that we know will wait?
--
Michael