Re: Adding a test for speculative insert abort case

Hi,

On 2019-05-15 20:35:49 -0700, Melanie Plageman wrote:
> > > I noticed that there is not a test case which would cover the speculative
> > > wait
> > > codepath. This seems much more challenging, however, it does seem like a
> > > worthwhile test to have.
> >
> > Shouldn't be that hard to create, I think. I think acquiring another
> > lock in a second, non-unique, expression index, ought to do the trick?
> > It probably has to be created after the unique index (so it's later in
> > the
> >
> >
> I would think that the sequence would be s1 and s2 probe the index, s1 and
> s2
> insert into the table, s1 updates the index but does not complete the
> speculative insert and clear the token (pause before
> table_complete_speculative). s2 is in speculative wait when attempting to
> update
> the index.
>
> Something like
>
> permutation
> "controller_locks"
> "controller_show"
> "s1_upsert" "s2_upsert"
> "controller_show"
> "controller_unlock_1_1" "controller_unlock_2_1"
> "controller_unlock_1_3" "controller_unlock_2_3"
> "controller_unlock_1_2"
> "s1_magically_pause_before_complete_speculative"
> # put s2 in speculative wait
> "controller_unlock_2_2"
> "s1_magically_unpause_before_complete_speculative"
>
> So, how would another lock on another index keep s1 from clearing the
> speculative token after it has updated the index?

If there were a second index on upserttest, something like CREATE INDEX
ON upserttest((blurt_and_lock2(key))); and blurt_and_lock2 acquired a
lock on (current_setting('spec.session')::int, 4), ISTM you could cause
a block to happen after the first index (the unique one, used for ON
CONFLICT) successfully created the index entry, but before
complete_speculative is called. Shouldn't that fulfil your
s1_magically_pause_before_complete_speculative goal? The
controller_locks would only acquire the (1, 4) lock, thereby *not*
blocking s2 (or you could just release the lock in a separate step).

Greetings,

Andres Freund