Fix connection reloading in development mode. [#4929 state:resolved]

Signed-off-by: José Valim <jose.valim@gmail.com>

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -144,7 +144,9 @@ module ActiveRecord
         @connections.each do |conn|
           conn.disconnect! if conn.requires_reloading?
         end
-        @connections = []
+        @connections.delete_if do |conn|
+          conn.requires_reloading?
+        end
       end
 
       # Verify active connections and remove and disconnect connections

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -142,9 +142,10 @@ module ActiveRecord
         # this should be overridden by concrete adapters
       end
 
-      # Returns true if its safe to reload the connection between requests for development mode.
+      # Returns true if its required to reload the connection between requests for development mode.
+      # This is not the case for Ruby/MySQL and it's not necessary for any adapters except SQLite.
       def requires_reloading?
-        true
+        false
       end
 
       # Checks whether the connection to the database is still active (i.e. not stale).