Re: [HACKERS] Parallel tuplesort (for parallel B-Tree index creation)

On Wed, Jan 24, 2018 at 5:59 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>> I am going to repeat my previous suggest that we use a Barrier here.
>>> Given the discussion subsequent to my original proposal, this can be a
>>> lot simpler than what I suggested originally. Each worker does
>>> BarrierAttach() before beginning to read tuples (exiting if the phase
>>> returned is non-zero) and BarrierArriveAndDetach() when it's done
>>> sorting. The leader does BarrierAttach() before launching workers and
>>> BarrierArriveAndWait() when it's done sorting.
>
> How does leader detect if one of the workers does BarrierAttach and
> then fails (either exits or error out) before doing
> BarrierArriveAndDetach?

If you attach and then exit cleanly, that's a programming error and
would cause anyone who runs BarrierArriveAndWait() to hang forever.
If you attach and raise an error, the leader will receive an error
message via CFI() and will then raise an error itself and terminate
all workers during cleanup.

--
Thomas Munro
http://www.enterprisedb.com