DEV: Add raw PG connection tracing behind an environment variable

This should be useful for debugging connection problems. Warning: this will generate some large files, and will likely impact performance

config/initializers/000-trace_pg_connections.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# Setting TRACE_PG_CONNECTIONS=1 will cause all pg connections
+# to be streamed to files for debugging. The filenames are formatted
+# like tmp/pgtrace/{{PID}}_{{CONNECTION_OBJECT_ID}}.txt
+#
+# Files will be automatically deleted when the connection is closed gracefully
+# (e.g. when activerecord closes it after a period of inactivity)
+# Files will not be automatically deleted when closed abruptly
+# (e.g. terminating/restarting the app process)
+#
+# Warning: this could create some very large files!
+
+if ENV["TRACE_PG_CONNECTIONS"]
+  PG::Connection.prepend(Module.new do
+    TRACE_DIR = "tmp/pgtrace"
+
+    def initialize(*args)
+      super(*args).tap do
+        FileUtils.mkdir_p(TRACE_DIR)
+        @trace_filename = "#{TRACE_DIR}/#{Process.pid}_#{self.object_id}.txt"
+        trace File.new(@trace_filename, "w")
+      end
+    end
+
+    def close
+      super.tap do
+        File.delete(@trace_filename)
+      end
+    end
+
+  end)
+end