Re: Weird test mixup

On Fri, Mar 15, 2024 at 11:23:31AM +0200, Heikki Linnakangas wrote:
> For the gin test, a single "SELECT injection_points_attach_local()" at the
> top of the test file would be most convenient.
> 
> If I have to do "SELECT
> injection_points_condition('gin-finish-incomplete-split', :'datname');" for
> every injection point in the test, I will surely forget it sometimes.

So will I, most likely..  The odds never play in favor of hackers.  I
have a few more tests in mind that can be linked to a specific
backend with SQL queries, but I've not been able to get back to it
yet.

> Wrt. the spinlock and shared memory handling, I think this would be simpler
> if you could pass some payload in the InjectionPointAttach() call, which
> would be passed back to the callback function:
> 
> In this case, the payload would be the "slot index" in shared memory.
>
> Or perhaps always allocate, say, 1024 bytes of working area for every
> attached injection point that the test module can use any way it wants. Like
> for storing extra conditions, or for the wakeup counter stuff in
> injection_wait(). A fixed size working area is a little crude, but would be
> very handy in practice.

Perhaps.  I am not sure that we need more than the current signature,
all that can just be handled in some module-specific shmem area.  The
key is to be able to link a point name to some state related to it.
Using a hash table would be more efficient, but performance wise a
array is not going to matter as there will most likely never be more
than 8 points.  4 is already a lot, just doubling that on safety
ground.

> It would be nice to automatically detach all the injection points on process
> exit. You wouldn't always want that, but I think most tests hold a session
> open throughout the test, and for those it would be handy.

Linking all the points to a PID with a injection_points_attach_local()
that switches a static flag while registering a before_shmem_exit() to
do an automated cleanup sounds like the simplest approach to me based
on what I'm reading on this thread.

(Just saw the buildfarm storm, wow.)
--
Michael