Introduction to NonStop SQL/MP

What Happens When a Query Is Submitted
NonStop SQL Architecture
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Figure 3-6. NonStop SQL/MP Components That Execute a Query
SQL File System
SQL Executor
Volume
Containing
Table A
Data Access
Manager
Volume
Containing
Table B
Data Access
Manager
Data access managers
evaluate and select
data from their
respective disk
volumes.
SQL executor joins
data selected from
the two tables.
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Application
Server Process
In Figure 3-6, a query requests a join of selected columns and rows from tables A and
B. As the figure suggests, NonStop SQL/MP pushes most of the work of data access
to the lowest level—the data access managers—and minimizes the amount of data that
needs to be evaluated at higher levels. The data access managers evaluate and select
the data from the tables residing on their respective disk volumes.
When the data access managers return data to the file system, the file system buffers
these responses before sending them to the executor.
The executor manipulates all the single-table requests in the query. In the example in
Figure 3-6, the executor implements the join of data retrieved from tables A and B.
If the data returned by the file system needs to be sorted, the executor performs the
sort. The executor uses an in-memory process, the user process sort (UPS), if the
returned data is less than or equal to 32,767 rows. For larger tasks, the executor calls
the FastSort utility to perform the sort.
Finally, the executor returns the results of the query to the host-language variables in
the application program or to the interface to the client program.