In the current Azure SQL Database Managed Instance (MI) preview, when customers create a new instance, they can allocate a certain number of CPU vCores and a certain amount of disk storage space for the instance. However, there is no explicit configuration option for the amount of memory allocated to the instance, because on MI, memory allocation is proportional to the number of vCores used.
How can a customer determine the actual amount of memory their MI instance can use, in GB? The answer is less obvious than it may seem. Using the traditional SQL Server methods will not provide the right answer on MI. In this article, we will go over the technical details of CPU and memory allocation on MI, and describe the correct way to answer this question.
The information and behavior described in this article are as of the time of writing (April 2018). Some aspects of MI behavior, including the visibility of certain compute resource allocations, may be temporary and will likely change as MI progresses from the current preview to general availability and beyond. Nevertheless, customers using MI in preview will find that this article answers some of the common questions about MI resource allocation.
What you see in SQL Server Management Studio is true, but it is also not the whole picture.