New option for Modis::Model - :enable_all_index

Allows to disable creating of my:core:key:all kind of keys if they are not needed.
Getting rid of these keys is important feature, because those keys consume a huge amount of memory
(one single *:all key for 158m records consumes for about of 10GB of ram)
Assuming some people don't use Model.all in their code,
it's important to disable that feature on demand

lib/modis/persistence.rb

@@ -61,6 +61,14 @@ def sti_base_key_for(id)
         "#{sti_base_absolute_namespace}:#{id}"
       end
 
+      def enable_all_index(bool)
+        @use_all_index = bool
+      end
+
+      def all_index_enabled?
+        @use_all_index == true || @use_all_index.nil?
+      end
+
       def create(attrs)
         model = new(attrs)
         model.save
@@ -128,8 +136,10 @@ def destroy
         run_callbacks :destroy do
           redis.pipelined do
             remove_from_indexes(redis)
-            redis.srem(self.class.key_for(:all), id)
-            redis.srem(self.class.sti_base_key_for(:all), id) if self.class.sti_child?
+            if self.class.all_index_enabled?
+              redis.srem(self.class.key_for(:all), id)
+              redis.srem(self.class.sti_base_key_for(:all), id) if self.class.sti_child?
+            end
             redis.del(key)
           end
         end
@@ -198,8 +208,10 @@ def persist
               future = attrs.any? ? redis.hmset(key, attrs) : :unchanged
 
               if new_record?
-                redis.sadd(self.class.key_for(:all), id)
-                redis.sadd(self.class.sti_base_key_for(:all), id) if self.class.sti_child?
+                if self.class.all_index_enabled?
+                  redis.sadd(self.class.key_for(:all), id)
+                  redis.sadd(self.class.sti_base_key_for(:all), id) if self.class.sti_child?
+                end
                 add_to_indexes(redis)
               else
                 update_indexes(redis)

spec/persistence_spec.rb

@@ -47,6 +47,10 @@ def test_before_save
       called_callbacks << :test_before_save
     end
   end
+
+  class MockModelNoAllIndex < MockModel
+    enable_all_index false
+  end
 end
 
 describe Modis::Persistence do
@@ -296,4 +300,22 @@ def test_before_save
       expect(model.update_attributes(name: nil)).to be false
     end
   end
+
+  describe 'key for all records' do
+    let(:all_key_name) { "#{PersistenceSpec::MockModel.absolute_namespace}:all" }
+
+    describe 'when :enable_all_index option is set to false' do
+      it 'does not save new record to the *:all key' do
+        model = PersistenceSpec::MockModel.create!(name: 'Sage')
+        expect(Redis.new.smembers(all_key_name).map(&:to_i)).to include(model.id)
+      end
+    end
+
+    describe 'when :enable_all_index option is set to false' do
+      it 'does not save new record to the *:all key' do
+        model = PersistenceSpec::MockModelNoAllIndex.create!(name: 'Alex')
+        expect(Redis.new.smembers(all_key_name).map(&:to_i)).to_not include(model.id)
+      end
+    end
+  end
 end