Update multiple appointment using Service.execute in CRM 2011

I have created a console application to update millions of records in a weekly basis. In which  some time sql time out issue and service proxy issue occured

In the C# code, I have used UpdateRequest class to update the entity. In the CRM 2011 before update roll up 12, there is no executemultiple class. So I can't use this feature. 

I have tried with Parallel.For (service.execute(updateRequest)) and normal c# for method both throws issue.

My goal is to update millions of records every week through console application. Could you please guide me?