Re: Unportable implementation of background worker start

Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> Tom Lane wrote:
>> It also appears to me that do_start_bgworker's treatment of fork
>> failure is completely brain dead. Did anyone really think about
>> that case?

> Hmm, I probably modelled it on autovacuum without giving that case much
> additional consideration.

Attached is a proposed patch that should make fork failure behave
sanely, ie it works much the same as a worker crash immediately after
launch. I also refactored things a bit to make do_start_bgworker
fully responsible for updating the RegisteredBgWorker's state,
rather than doing just some of it as before.

I tested this by hot-wiring the fork_process call to fail some of
the time, which showed that the postmaster now seems to recover OK,
but parallel.c's logic is completely innocent of the idea that
worker-startup failure is possible. The leader backend just freezes,
and nothing short of kill -9 on that backend will get you out of it.
Fixing that seems like material for a separate patch though.

regards, tom lane