Segfault while connecting from multiple processes with Postgres 12

[jessebs]

I'm running Postgres 12.1, Ruby 2.6.5 and pg 1.1.4 on MacOS Catalina. This also happens on Ruby 2.5.1 and 2.5.7 as well as MacOS Mojave. It does not happen with Postgres 10 or 11.

Running the following small script will cause a segfault.

#!/usr/bin/env ruby
require 'pg'

PG.connect(:host => 'localhost', :user => 'username', :dbname => 'test_db')

Process.fork do
  PG.connect(:host => 'localhost', :user => 'username', :dbname => 'test_db')
end

See the attached segfault.txt and crash_report.txt

[konung]

Confirming the same issue. Ran into it while testing on my MacOS an app, after upgrading to Postgres 12 from Postgres 11 ( via brew) . Works for a Single connection, but crashes for multiple, i.e. crashes a Rails app, when trying to load models.

gem 'pg' => PG::VERSION = "1.1.4"
rails 6.0.1
ruby 2.6.5 (also tried 2.5.3 with the same result)
psql (PostgreSQL) 12.1
MacOS Catalina

The only thing that changed - upgraded Postrgres to 12.1 from 11

[cbandy]

@jessebs I expect gssencmode: "disable" will avoid the crash. Can you please verify?

[jessebs]

Yes, that did avoid the issue.

[cbandy]

I've reported this upstream: https://postgr.es/m/93f7379b-2e2f-db0c-980e-07ebd5de92ff%40crunchydata.com

[trevorcreech]

It looks like in Rails 5, this can be fixed by adding gssencmode: disable as a connection parameter in database.yml

Unfortunately Rails 4 doesn't pass gssencmode along to pg (because VALID_CONN_PARAMS is hardcoded until Rails 5). We were able to fix this by setting a PGGSSENCMODE="disable" environment variable.

[miguelpeniche]

Thanks a lot @trevorcreech, ENV variable PGGSSENCMODE="disable" worked for me.

[jessebs]

I'm a bit confused - based on my understanding of the problem, I would expect that closing the connection before the fork would resolve it but it does not.

Any understanding of why that's the case?

[cbandy]

It's not about shared handles or anything. It seems that macOS libraries are generally not safe to use after fork() (due to libdispatch.) It's a known issue over at Homebrew.

[alienxp03]

Another workaround that I found is by not setting any value to the host, or just omit the host params.

# 1
Process.fork do
  PG.connect(:host => '', :user => 'username', :dbname => 'test_db')
end

# 2
Process.fork do
  PG.connect(:user => 'username', :dbname => 'test_db')
end

If you're in Rails, you can just do the same thing with the host params.

# 1: This will crash
development:
  adapter: postgresql
  database: my_database
  host: localhost

# 2: This won't crash and will still connect to localhost just fine
development:
  adapter: postgresql
  database: my_database
  host:

So far I noticed that I only need this workaround if the host is localhost or 127.0.0.1.

[cbandy]

@alienxp03 Yes, this also skips GSS encryption by connecting over Unix socket (which is only available when client and server are on the same machine.) Depending on how the server is configured, Unix socket may involve different authentication than TCP socket.