don't send nils to cassandra driver on eventstream insert

During the EventStream refactor we changed the page view inserts from
using PageView#changes to PageView#attributes. This was the right thing
to do, because #changes won't include columns that have the
default value for that column, but cassandra needs to be given any
non-nil default values. Not a problem for PageView, but it could be for
other models.

However, this introduced a performance regression, because #attributes
includes nil attributes which means the cassandra driver was sending a
DELETE (list of columns) command, creating a new tombstone record in
cassandra. The new insert_record() method on the driver removes any nil
values before calling update_record.

test plan: enable cassandra page views, then visit some pages. after the
insert job runs, the page views should have been created properly and
still display properly in the history.

Change-Id: Iccb967d3ec1f6b295d98b3f330b4b8ffe4508437
Reviewed-on: https://gerrit.instructure.com/20151
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>

lib/canvas/cassandra.rb

@@ -148,6 +148,14 @@ module Canvas::Cassandra
       end
     end
 
+    # same as update_record, but preferred when doing inserts -- it skips
+    # updating columns with nil values, rather than creating tombstone delete
+    # records for them
+    def insert_record(table_name, primary_key_attrs, changes)
+      changes = changes.reject { |k,v| v.is_a?(Array) ? v.last.nil? : v.nil? }
+      update_record(table_name, primary_key_attrs, changes)
+    end
+
     def select_value(query, *args)
       result_row = execute(query, *args).fetch
       result_row && result_row.to_hash.values.first

lib/event_stream.rb

@@ -39,7 +39,7 @@ class EventStream
 
   def insert(record)
     database.batch do
-      database.update_record(table, { id_column => record.id }, record.attributes)
+      database.insert_record(table, { id_column => record.id }, record.attributes)
       run_callbacks(:insert, record)
     end
   end

spec/lib/canvas/cassandra_spec.rb

@@ -145,6 +145,18 @@ describe "Canvas::Redis::Cassandra" do
     end
   end
 
+  describe "#insert_record" do
+    it "should not delete nils in an AR#attributes style hash" do
+      db.expects(:execute).with("UPDATE test_table SET name = ? WHERE id = ?", "test", 5)
+      db.insert_record("test_table", { :id => 5 }, { :name => "test", :nick => nil })
+    end
+
+    it "should not delete nils in an AR#changes style hash" do
+      db.expects(:execute).with("UPDATE test_table SET name = ? WHERE id = ?", "test", 5)
+      db.insert_record("test_table", { :id => 5 }, { :name => [nil, "test"], :nick => [nil, nil] })
+    end
+  end
+
   describe "execute and update" do
     it_should_behave_like "cassandra page views"
 

spec/lib/event_stream_spec.rb

@@ -24,6 +24,7 @@ describe EventStream do
     @database = stub('database')
     def @database.batch; yield; end
     def @database.update_record(*args); end
+    def @database.insert_record(*args); end
     def @database.update(*args); end
     ::Canvas::Cassandra::Database.stubs(:from_config).with(@database_name.to_s).returns(@database)
   end
@@ -129,24 +130,24 @@ describe EventStream do
       end
 
       it "should insert into the configured database" do
-        @database.expects(:update_record).once
+        @database.expects(:insert_record).once
         @stream.insert(@record)
       end
 
       it "should insert into the configured table" do
-        @database.expects(:update_record).with(@table.to_s, anything, anything)
+        @database.expects(:insert_record).with(@table.to_s, anything, anything)
         @stream.insert(@record)
       end
 
       it "should insert by the record's id into the configured id column" do
         id_column = stub(:to_s => stub('id_column'))
         @stream.id_column id_column
-        @database.expects(:update_record).with(anything, { id_column.to_s => @record.id }, anything)
+        @database.expects(:insert_record).with(anything, { id_column.to_s => @record.id }, anything)
         @stream.insert(@record)
       end
 
       it "should insert the record's attributes" do
-        @database.expects(:update_record).with(anything, anything, @record.attributes)
+        @database.expects(:insert_record).with(anything, anything, @record.attributes)
         @stream.insert(@record)
       end
 
@@ -154,7 +155,7 @@ describe EventStream do
         spy = stub('spy')
         @stream.on_insert{ spy.trigger }
         @database.expects(:batch).once
-        @database.expects(:update_record).never
+        @database.expects(:insert_record).never
         spy.expects(:trigger).never
         @stream.insert(@record)
       end