How to deal with ruby and postgres segmentation fault on MacOS when using macports or homebrew.md

Here's something I spent a long time debugging, so I'm making this gist to help others find the solution when searching.

Summary

postgres 12 on MacOS will cause crashes when forking. The solution is to do one of these two things:

add gssencmode: "disable" to database.yml
if using homebrew: uninstall postgres, update homebrew, reinstall postgres

Here's some discussion:

How does the bug happen and what does it look like

macos
ruby on rails
web server like puma or unicorn configured to fork
postgres 12 installed by homebrew or macports (homebrew has now been fixed)

you'll see this at the top:

/Users/john/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/listen-3.2.1/lib/listen/record/entry.rb:53: [BUG] Segmentation fault at 0x0000000000000110
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin19]

-- Crash Report log information --------------------------------------------
   See Crash Report log file under the one of following:
     * ~/Library/Logs/DiagnosticReports
     * /Library/Logs/DiagnosticReports
   for more details.
Don't forget to include the above Crash Report log file in bug reports.

-- Control frame information -----------------------------------------------

This at the bottom:

[IMPORTANT]
Don't forget to include the Crash Report log file under
DiagnosticReports directory in bug reports.

And this in ~/Library/Logs/DiagnosticReports

Process:               ruby [2193]
Path:                  /Users/USER/*/ruby
Identifier:            ruby
Version:               0
Code Type:             X86-64 (Native)
Parent Process:        ruby [2128]
Responsible:           iTerm2 [717]
User ID:               502

Date/Time:             2020-04-28 22:44:44.737 -0400
OS Version:            Mac OS X 10.15.4 (19E287)
Report Version:        12
Anonymous UUID:        C0DC3E8B-79F0-D22B-DEB4-7E21ED4CF508


Time Awake Since Boot: 170 seconds

System Integrity Protection: enabled

Crashed Thread:        5  thread_pool.rb*  Dispatch queue: com.apple.security.keychain-cache-queue

Exception Type:        EXC_BAD_ACCESS (SIGABRT)
Exception Codes:       KERN_INVALID_ADDRESS at 0x0000000000000110
Exception Note:        EXC_CORPSE_NOTIFY

VM Regions Near 0x110:
-->
    __TEXT                 0000000108e77000-0000000108e78000 [    4K] r-x/r-x SM=COW  /Users/USER/*

Application Specific Information:
*** multi-threaded process forked ***
crashed on child side of fork pre-exec

probably the most interesting line is:

Crashed Thread: 5 thread_pool.rb* Dispatch queue: com.apple.security.keychain-cache-queue

jjb/How to deal with ruby and postgres segmentation fault on MacOS when using macports or homebrew.md

Summary

How does the bug happen and what does it look like