Prevent unnecessary `select`s and `remove_key`s

lib/gitlab/shell.rb

@@ -248,12 +248,14 @@ module Gitlab
       return unless self.authorized_keys_enabled?
 
       batch_read_key_ids do |ids_in_file|
+        ids_in_file.uniq!
         keys_in_db = Key.where(id: ids_in_file)
-        if ids_in_file.size > keys_in_db.count
-          ids_to_remove = ids_in_file - keys_in_db.pluck(:id)
-          ids_to_remove.each do |id|
-            remove_key("key-#{id}")
-          end
+
+        return unless ids_in_file.size > keys_in_db.count # optimization
+
+        ids_to_remove = ids_in_file - keys_in_db.pluck(:id)
+        ids_to_remove.each do |id|
+          remove_key("key-#{id}")
         end
       end
     end

spec/lib/gitlab/shell_spec.rb

@@ -289,6 +289,43 @@ describe Gitlab::Shell, lib: true do
         expect(find_in_authorized_keys_file(@another_key.id)).to be_truthy
       end
     end
+
+    context 'when keys there are duplicate keys in the file that are not in the DB' do
+      before do
+        gitlab_shell.remove_all_keys
+        gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+        gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+      end
+
+      it 'removes the keys' do
+        expect(find_in_authorized_keys_file(1234)).to be_truthy
+        gitlab_shell.remove_keys_not_found_in_db
+        expect(find_in_authorized_keys_file(1234)).to be_falsey
+      end
+
+      it 'does not run remove more than once per key (in a batch)' do
+        expect(gitlab_shell).to receive(:remove_key).with('key-1234').once
+        gitlab_shell.remove_keys_not_found_in_db
+      end
+    end
+
+    context 'when keys there are duplicate keys in the file that ARE in the DB' do
+      before do
+        gitlab_shell.remove_all_keys
+        @key = create(:key)
+        gitlab_shell.add_key(@key.shell_id, @key.key)
+      end
+
+      it 'does not remove the key' do
+        gitlab_shell.remove_keys_not_found_in_db
+        expect(find_in_authorized_keys_file(@key.id)).to be_truthy
+      end
+
+      it 'does not need to run a SELECT query for that batch, on account of that key' do
+        expect_any_instance_of(ActiveRecord::Relation).not_to receive(:pluck)
+        gitlab_shell.remove_keys_not_found_in_db
+      end
+    end
   end
 
   describe '#batch_read_key_ids' do