Support Rails 6 `insert_all!`

This fixes Load Balancing implementation
to support and test `insert_all!`

changelogs/unreleased/ee-insert-all-for-load-balancing.yml

+---
+title: Support Rails 6 `insert_all!`
+merge_request: 26595
+author:
+type: fixed

ee/lib/gitlab/database/load_balancing/connection_proxy.rb

@@ -23,15 +23,16 @@ module Gitlab
           update_all
         ).freeze
 
+        NON_STICKY_READS = %i(
+          select
+          quote_column_name
+        ).freeze
+
         # hosts - The hosts to use for load balancing.
         def initialize(hosts = [])
           @load_balancer = LoadBalancer.new(hosts)
         end
 
-        def select(*args)
-          read_using_load_balancer(:select, args)
-        end
-
         def select_all(arel, name = nil, binds = [], preparable: nil)
           if arel.respond_to?(:locked) && arel.locked
             # SELECT ... FOR UPDATE queries should be sent to the primary.
@@ -42,6 +43,12 @@ module Gitlab
           end
         end
 
+        NON_STICKY_READS.each do |name|
+          define_method(name) do |*args, &block|
+            read_using_load_balancer(name, args, &block)
+          end
+        end
+
         STICKY_WRITES.each do |name|
           define_method(name) do |*args, &block|
             write_using_load_balancer(name, args, sticky: true, &block)

ee/spec/lib/gitlab/database/load_balancing/connection_proxy_spec.rb

@@ -44,6 +44,17 @@ describe Gitlab::Database::LoadBalancing::ConnectionProxy do
     end
   end
 
+  Gitlab::Database::LoadBalancing::ConnectionProxy::NON_STICKY_READS.each do |name|
+    describe "#{name}" do
+      it 'runs the query on the replica' do
+        expect(proxy).to receive(:read_using_load_balancer)
+          .with(name, ['foo'])
+
+        proxy.send(name, 'foo')
+      end
+    end
+  end
+
   Gitlab::Database::LoadBalancing::ConnectionProxy::STICKY_WRITES.each do |name|
     describe "#{name}" do
       it 'runs the query on the primary and sticks to it' do
@@ -55,6 +66,45 @@ describe Gitlab::Database::LoadBalancing::ConnectionProxy do
     end
   end
 
+  describe '.insert_all!' do
+    before do
+      ActiveRecord::Schema.define do
+        create_table :connection_proxy_bulk_insert, force: true do |t|
+          t.string :name, null: true
+        end
+      end
+    end
+
+    after do
+      ActiveRecord::Schema.define do
+        drop_table :connection_proxy_bulk_insert, force: true
+      end
+    end
+
+    let(:model_class) do
+      Class.new(ApplicationRecord) do
+        self.table_name = "connection_proxy_bulk_insert"
+      end
+    end
+
+    it 'inserts data in bulk' do
+      expect(model_class).to receive(:connection)
+        .at_least(:once)
+        .and_return(proxy)
+
+      expect(proxy).to receive(:write_using_load_balancer)
+        .at_least(:once)
+        .and_call_original
+
+      expect do
+        model_class.insert_all! [
+          { name: "item1" },
+          { name: "item2" }
+        ]
+      end.to change { model_class.count }.by(2)
+    end
+  end
+
   # We have an extra test for #transaction here to make sure that nested queries
   # are also sent to a primary.
   describe '#transaction' do