Re: Wait for parallel workers to attach

On Sat, Jan 27, 2018 at 3:14 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> During the recent development of parallel operation (parallel create
> index)[1], a need has been arised for $SUBJECT. The idea is to allow
> leader backend to rely on number of workers that are successfully
> started. This API allows leader to wait for all the workers to start
> or fail even if one of the workers fails to attach. We consider
> workers started/attached once they are attached to error queue. This
> will ensure that any error after the workers are attached won't be
> silently ignored by leader.

known_started_workers looks a lot like any_message_received. Perhaps
any_message_received should be renamed to known_started_workers and
reused here. After all, if we know that a worker was started, there's
no need for WaitForParallelWorkersToFinish to again call
GetBackgroundWorkerPid() for it.

I think that you shouldn't need the 10ms delay loop; waiting forever
should work. If a work fails to start, the postmaster should send
SIGUSR1 which should set our latch.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company