Introduction to NonStop SQL/MP

Other Architectural Features
NonStop SQL Architecture
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Single-Table Query Evaluation
The data access manager performs single-table query evaluations (requests) against
the data on its disk volume. Each evaluation is a simple selection expression
consisting of ORs, ANDs, and other simple operators evaluated against literals and
columns. The data access manager filters and groups the data it retrieves from disk,
returning only the qualified data to the file system. It can also perform aggregations.
By returning only the data needed for the result, the data access manager reduces
message traffic and improves query performance. Reducing message traffic is even
more important when the executor requests data residing at a remote location and the
returned data must travel across the network.
For example, suppose you want to know the locations and quantity on hand of a
group of related parts in your inventory database. The related part numbers are
between 2000 and 2010. Consider the following query:
SELECT LOC,
PARTNAME, QTY
FROM INVENT
WHERE PARTNUM BETWEEN 2000 AND 2010 ;
The INVENT table is partitioned across geographically distributed systems, as is the
PARTLOC table shown in Figure 3-3. The INVENT table, however, contains 30
columns instead of 3.
Figure 3-8 shows how the data access manager executes its part of the preceding
query, evaluating a large amount of data and efficiently returning a very small result.