Introduction to NonStop SQL/MP

3 NonStop SQL/MP Architecture
113425 Tandem Computers Incorporated 3–1
This section describes the physical structure of a NonStop SQL/MP database and the
way the logical and physical structures are linked through the NonStop SQL/MP data
dictionary. The section then describes the basic physical components: files, table
organizations, indexes, and partitions. Next, it explains how an SQL query is
compiled and executed, showing how NonStop SQL/MP optimizes a query plan to
achieve the best performance. Finally, the section examines other architectural
features such as parallel query execution, the data access manager, and sequential
block buffering.
Physical Database
Structure
A database has a logical and a physical structure. The tables and views that you see
and manipulate directly through the SQL language are the logical structure (logical
schema). Underlying the logical database is a set of physical files on disks managed by
the SQL file system and accessed through the data access manager (DP2 disk process).
Logical Schema The logical schema represents the business information contained in the database. The
logical schema includes the database elements (such as columns, rows, tables, and
views) that you can query using SQL statements.
The definitions of these elements, and their relationships to one another, are stored in
the NonStop SQL/MP data dictionary. The data dictionary also records the
relationships between the logical elements and the corresponding physical objects.
The data dictionary consists of the SQL catalogs, sets of relational SQL tables that
describe the database objects, and the corresponding file labels, which describe the
underlying physical files and also contain catalog information.
Physical Structure When you insert data into a table (or an associated protection view), you are actually
storing data in a physical file in the Guardian environment. Every table, and indirectly
every view, is associated with one or more files. The files are the physical storage
structures that hold the data in a database.
Figure 3-1 illustrates this two-level structure.