Understanding Memory - SQL Server 2012 Internals and Troubleshooting - page 63

SQL SERVER MEMORY
The i rst part of this chapter dealt mainly with the memory environment external to SQL Server —
that is, understanding and coni guring memory before SQL Server starts. This second part looks at
how SQL Server manages memory.
DROPPING WINDOWS SERVER 2003 SUPPORT
SQL Server 2012 doesn't support Window Server 2003, which was a huge relief for
the SQL Server development team, as it enabled them to drop all the code required
to deal with legacy memory models used prior to Windows Server 2008.
The effect of this is lower development costs for Microsoft (and therefore quicker
product releases) and an increase in the efi ciency with which SQL Server can be
supported.
Memory management in SQL Server has a three-level structure. At the bottom are memory nodes,
which are the lowest-level allocators for SQL Server memory. The second level consists of memory
clerks, which are used to access the memory nodes, and cache stores, which are used for caching.
The top level contains memory objects, which provide a smaller degree of granularity than the
memory clerks allow directly.
Only clerks can access memory nodes to allocate memory, so every component that needs to allocate
substantial amounts of memory needs to create its own memory clerk when the SQL Server service
starts.
NEW MEMORY MANAGER FOR SQL SERVER 2012
Previous versions of SQL Server required VAS space outside of SQL Server's memory
allocation for Multi-Page Allocations (MPA) and CLR memory requirements.
The MPA was used whenever a component required a single allocation greater than
8KB and a single page allocator dealt with anything less than or equal to 8KB. In
SQL Server 2012, there is only one page allocator for all requests and they all come
directly from SQL Server's memory allocation.
CLR allocations also come directly from SQL Server's memory allocation in SQL
Server 2012, which makes it much easier to size SQL Server's memory requirements
(See Min and Max Server Memory later in the chapter).