Cache database version in schema cache

  * The database version will get cached in the schema cache file during the
    schema cache dump. When the database version check happens, the version will
    be pulled from the schema cache and thus avoid querying the database for
    the version.
  * If the schema cache file doesn't exist, we'll query the database for the
    version and cache it on the schema cache object.
  * To facilitate this change, all connection adapters now implement
    #get_database_version and #database_version. #database_version returns the
    value from the schema cache.
  * To take advantage of the cached database version, the database version check
    will now happen after the schema cache is set on the connection in the
    connection pool.

1 files changed, 28 insertions, 2 deletions

diff --git a/activerecord/test/cases/connection_adapters/schema_cache_test.rb b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
index 5113548091..89a9c30f9b 100644
--- a/activerecord/test/cases/connection_adapters/schema_cache_test.rb
+++ b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
@@ -6,8 +6,9 @@ module ActiveRecord
   module ConnectionAdapters
     class SchemaCacheTest < ActiveRecord::TestCase
       def setup
-        @connection = ActiveRecord::Base.connection
-        @cache      = SchemaCache.new @connection
+        @connection       = ActiveRecord::Base.connection
+        @cache            = SchemaCache.new @connection
+        @database_version = @connection.get_database_version
       end
 
       def test_primary_key
@@ -28,6 +29,7 @@ module ActiveRecord
           assert new_cache.data_sources("posts")
           assert_equal "id", new_cache.primary_keys("posts")
           assert_equal 1, new_cache.indexes("posts").size
+          assert_equal @database_version.to_s, new_cache.database_version.to_s
         end
       end
 
@@ -55,6 +57,20 @@ module ActiveRecord
         @connection.schema_cache = old_cache
       end
 
+      def test_yaml_loads_5_1_dump_without_database_version_still_queries_for_database_version
+        @cache = YAML.load(File.read(schema_dump_path))
+
+        # Simulate assignment in railtie after loading the cache.
+        old_cache, @connection.schema_cache = @connection.schema_cache, @cache
+
+        # We can't verify queries get executed because the database version gets
+        # cached in both MySQL and PostgreSQL outside of the schema cache.
+        assert_nil @cache.instance_variable_get(:@database_version)
+        assert_equal @database_version.to_s, @cache.database_version.to_s
+      ensure
+        @connection.schema_cache = old_cache
+      end
+
       def test_primary_key_for_non_existent_table
         assert_nil @cache.primary_keys("omgponies")
       end
@@ -74,6 +90,14 @@ module ActiveRecord
         assert_equal indexes, @cache.indexes("posts")
       end
 
+      def test_caches_database_version
+        @cache.database_version # cache database_version
+
+        assert_no_queries do
+          assert_equal @database_version.to_s, @cache.database_version.to_s
+        end
+      end
+
       def test_clearing
         @cache.columns("posts")
         @cache.columns_hash("posts")
@@ -84,6 +108,7 @@ module ActiveRecord
         @cache.clear!
 
         assert_equal 0, @cache.size
+        assert_nil @cache.instance_variable_get(:@database_version)
       end
 
       def test_dump_and_load
@@ -101,6 +126,7 @@ module ActiveRecord
           assert @cache.data_sources("posts")
           assert_equal "id", @cache.primary_keys("posts")
           assert_equal 1, @cache.indexes("posts").size
+          assert_equal @database_version.to_s, @cache.database_version.to_s
         end
       end