SQL Server Architecture - SQL Server 2012 Internals and Troubleshooting - page 12

Figure 1-4 shows the addition of the query plan as the output from the Optimizer being passed
to the Query Executor. Also introduced is the Storage Engine, which is interfaced by the Query
Executor via OLE DB to the Access Methods (coming up next).

Query Tree Language Event

Cmd Parser TDS

Query Plan

SQL Server
Network Interface

Optimizer Query Executor SNI

Protocol
Layer

Relational Engine

Plan Cache

OLE DB

Access Methods

Storage Engine Bufer Pool

FIGURE 1-4

Access Methods
Access Methods is a collection of code that provides the storage structures for your data and
indexes, as well as the interface through which data is retrieved and modii ed. It contains all the
code to retrieve data but it doesn't actually perform the operation itself; it passes the request to the
Buffer Manager.

Suppose our SELECT statement needs to read just a few rows that are all on a single page. The Access
Methods code will ask the Buffer Manager to retrieve the page so that it can prepare an OLE DB
rowset to pass back to the Relational Engine.

Buf er Manager
The Buffer Manager, as its name suggests, manages the buffer pool, which represents the majority of
SQL Server's memory usage. If you need to read some rows from a page (you'll look at writes when
we look at an UPDATE query), the Buffer Manager checks the data cache in the buffer pool to see if