Configure query caching (per thread) on the connection pool

4 files changed, 71 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index e9ecb78e27..8ce28eae62 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -307,6 +307,7 @@ module ActiveRecord
       end
 
       include MonitorMixin
+      include QueryCache::ConnectionPoolConfiguration
 
       attr_accessor :automatic_reconnect, :checkout_timeout, :schema_cache
       attr_reader :spec, :connections, :size, :reaper
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 d4229dfdba..7eab7de5d3 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 +4,8 @@ module ActiveRecord
       class << self
         def included(base) #:nodoc:
           dirties_query_cache base, :insert, :update, :delete, :rollback_to_savepoint, :rollback_db_transaction
+
+          base.set_callback :checkout, :after, :configure_query_cache!
           base.set_callback :checkin, :after, :disable_query_cache!
         end
 
@@ -19,6 +21,27 @@ module ActiveRecord
         end
       end
 
+      module ConnectionPoolConfiguration
+        def initialize(*)
+          super
+          @query_cache_enabled = Concurrent::Map.new { false }
+        end
+
+        def enable_query_cache!
+          @query_cache_enabled[connection_cache_key(Thread.current)] = true
+          connection.enable_query_cache! if active_connection?
+        end
+
+        def disable_query_cache!
+          @query_cache_enabled.delete connection_cache_key(Thread.current)
+          connection.disable_query_cache! if active_connection?
+        end
+
+        def query_cache_enabled
+          @query_cache_enabled[connection_cache_key(Thread.current)]
+        end
+      end
+
       attr_reader :query_cache, :query_cache_enabled
 
       def initialize(*)
@@ -98,6 +121,10 @@ module ActiveRecord
         def locked?(arel)
           arel.respond_to?(:locked) && arel.locked
         end
+
+        def configure_query_cache!
+          enable_query_cache! if pool.query_cache_enabled
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index 667bfe96f6..ec246e97bc 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -24,10 +24,17 @@ module ActiveRecord
     end
 
     def self.run
-      ActiveRecord::Base.connection.enable_query_cache!
+      caching_pool = ActiveRecord::Base.connection_pool
+      caching_was_enabled = caching_pool.query_cache_enabled
+
+      caching_pool.enable_query_cache!
+
+      [caching_pool, caching_was_enabled]
     end
 
-    def self.complete(_)
+    def self.complete((caching_pool, caching_was_enabled))
+      caching_pool.disable_query_cache! unless caching_was_enabled
+
       ActiveRecord::Base.connection_handler.connection_pool_list.each do |pool|
         pool.release_connection if pool.active_connection? && !pool.connection.transaction_open?
       end
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index 5b0477aabe..90054ce83d 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -313,6 +313,40 @@ class QueryCacheTest < ActiveRecord::TestCase
     end
   end
 
+  def test_query_cache_does_not_establish_connection_if_unconnected
+    ActiveRecord::Base.clear_active_connections!
+    refute ActiveRecord::Base.connection_handler.active_connections? # sanity check
+
+    middleware {
+      refute ActiveRecord::Base.connection_handler.active_connections?, "QueryCache forced ActiveRecord::Base to establish a connection in setup"
+    }.call({})
+
+    refute ActiveRecord::Base.connection_handler.active_connections?, "QueryCache forced ActiveRecord::Base to establish a connection in cleanup"
+  end
+
+  def test_query_cache_is_enabled_on_connections_established_after_middleware_runs
+    ActiveRecord::Base.clear_active_connections!
+    refute ActiveRecord::Base.connection_handler.active_connections? # sanity check
+
+    middleware {
+      assert ActiveRecord::Base.connection.query_cache_enabled, "QueryCache did not get lazily enabled"
+    }.call({})
+  end
+
+  def test_query_caching_is_local_to_the_current_thread
+    ActiveRecord::Base.clear_active_connections!
+
+    middleware {
+      assert ActiveRecord::Base.connection_pool.query_cache_enabled
+      assert ActiveRecord::Base.connection.query_cache_enabled
+
+      Thread.new {
+        refute ActiveRecord::Base.connection_pool.query_cache_enabled
+        refute ActiveRecord::Base.connection.query_cache_enabled
+      }.join
+    }.call({})
+  end
+
   private
     def middleware(&app)
       executor = Class.new(ActiveSupport::Executor)