DEV: Use MiniSql ActiveRecordPostgres adapter (#15767)

This adapter ensures that MiniSql locks the ActiveRecord mutex before using the raw PG connection. This ensures that multiple threads will not attempt to use the same connection simultaneously.

This commit also removes the schema_cache_concurrency freedom-patch, which is no longer required now that cross-thread connection use is controlled by the mutex.

For the original root cause of this issue, see https://github.com/rails/rails/pull/38577

Gemfile.lock

@@ -236,7 +236,7 @@ GEM
       libv8-node (~> 16.10.0.0)
     mini_scheduler (0.13.0)
       sidekiq (>= 4.2.3)
-    mini_sql (1.1.3)
+    mini_sql (1.3.0)
     mini_suffix (0.3.3)
       ffi (~> 1.9)
     minitest (5.15.0)

lib/freedom_patches/schema_cache_concurrency.rb

@@ -1,27 +0,0 @@
-# frozen_string_literal: true
-#
-# Rails has a circular dependency in SchemaCache.
-# In certain situation SchemaCache can carry a @connection
-# from a different thread. This causes potential concurrency bugs
-# in Sidekiq.
-#
-# This patches it so it is less flexible (theoretically) but always bound to the current connection
-
-# This patch needs to be reviewed in future versions of Rails.
-# We should consider upstreaming this optionally.
-
-module ActiveRecord
-  module ConnectionAdapters
-    class SchemaCache
-
-      def connection=(connection)
-        # AbstractPool get_schema_cache does schema_cache.connection = connection
-        Thread.current["schema_cached_connection"] = connection
-      end
-
-      def connection
-        Thread.current["schema_cached_connection"]
-      end
-    end
-  end
-end

lib/mini_sql_multisite_connection.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class MiniSqlMultisiteConnection < MiniSql::Postgres::Connection
+class MiniSqlMultisiteConnection < MiniSql::ActiveRecordPostgres::Connection
 
   class CustomBuilder < MiniSql::Builder
 
@@ -78,8 +78,8 @@ class MiniSqlMultisiteConnection < MiniSql::Postgres::Connection
 
   # we need a tiny adapter here so we always run against the
   # correct multisite connection
-  def raw_connection
-    ActiveRecord::Base.connection.raw_connection
+  def active_record_connection
+    ActiveRecord::Base.connection
   end
 
   # make for a multisite friendly prepared statement cache