Philip White <philip@mailworks.org> writes:
> I am experiencing a startup failure on OS X 10.11.3, with PostgreSQL 9.5.1 that I installed using Homebrew.
> ...
> FATAL: postmaster became multithreaded during startup
> HINT: Set the LC_ALL environment variable to a valid locale.
Hm. The HINT is reflecting the one known cause of this problem,
but perhaps you've stumbled across a new one :-(.
The other theory that comes to mind is that maybe Homebrew's build
of Postgres has modified things in a way that breaks for you.
Neither thought leads to any quick fixes. The best idea I can
suggest is to strace the postmaster and try to identify where
it's cloning an additional thread. OS X doesn't have strace
that I know of, but googling suggests you can get similar
results with dtruss. If you run with -d 5 as you did here,
the debug printouts (which should be captured by dtruss too)
will provide landmarks to help identify where it goes wrong.
Please post back with the dtruss log (and pg_config output
might be helpful too) and we'll see if we can make sense of it.
regards, tom lane