Re: BUG #15290: Stuck Parallel Index Scan query

On 2018-07-25 14:04:11 +1200, Thomas Munro wrote:
> Ok, I see it:
> 
>                         /* check for interrupts while we're not
> holding any buffer lock */
>                         CHECK_FOR_INTERRUPTS();
>                         /* step right one page */
>                         so->currPos.buf = _bt_getbuf(rel, blkno, BT_READ);
>                         ...
>                         /* nope, keep going */
>                         if (scan->parallel_scan != NULL)
>                         {
>                                 status = _bt_parallel_seize(scan, &blkno);
> 
> That leads to a condition variable wait, while we still hold that
> buffer lock.  That prevents interrupts.  Oops.

Heh, guessed right.  I kinda wonder if we shouldn't add a
CHECK_FOR_INTERRUPTS_FOR_REALZ() that asserts if interrupts aren't
held. There are plenty places where we rely on that being the case, for
correctness.

Greetings,

Andres Freund