Clear query cache during checkin, instead of an execution callback

It doesn't make sense for the query cache to persist while a connection
moves through the pool and is assigned to a new thread.

[Samuel Cochran & Matthew Draper]

3 files changed, 7 insertions, 12 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
index 2f8a89e88e..3eac1b66ae 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
@@ -4,6 +4,7 @@ module ActiveRecord
       class << self
         def included(base) #:nodoc:
           dirties_query_cache base, :insert, :update, :delete, :rollback_to_savepoint, :rollback_db_transaction
+          base.set_callback :checkin, :after, :disable_query_cache!
         end
 
         def dirties_query_cache(base, *method_names)
@@ -41,6 +42,7 @@ module ActiveRecord
 
       def disable_query_cache!
         @query_cache_enabled = false
+        clear_query_cache
       end
 
       # Disable the query cache within the block.
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 0c7197a002..2296df4481 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -62,17 +62,17 @@ module ActiveRecord
     # notably, the instance methods provided by SchemaStatements are very useful.
     class AbstractAdapter
       ADAPTER_NAME = "Abstract".freeze
+      include ActiveSupport::Callbacks
+      define_callbacks :checkout, :checkin
+
       include Quoting, DatabaseStatements, SchemaStatements
       include DatabaseLimits
       include QueryCache
-      include ActiveSupport::Callbacks
       include ColumnDumper
       include Savepoints
 
       SIMPLE_INT = /\A\d+\z/
 
-      define_callbacks :checkout, :checkin
-
       attr_accessor :visitor, :pool
       attr_reader :schema_cache, :owner, :logger
       alias :in_use? :owner
diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index c42c22ab09..23dae825c2 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -24,17 +24,10 @@ module ActiveRecord
     end
 
     def self.run
-      connection    = ActiveRecord::Base.connection
-      enabled       = connection.query_cache_enabled
-      connection.enable_query_cache!
-
-      [connection, enabled]
+      ActiveRecord::Base.connection.enable_query_cache!
     end
 
-    def self.complete((connection, enabled))
-      connection.clear_query_cache
-      connection.disable_query_cache! unless enabled
-
+    def self.complete(_)
       unless ActiveRecord::Base.connected? && ActiveRecord::Base.connection.transaction_open?
         ActiveRecord::Base.clear_active_connections!
       end