SQL/MP Installation and Management Guide

Enhancing Performance
HP NonStop SQL/MP Installation and Management Guide—523353-004
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Creating Logical Views of Data
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Constraints simplify the change process to a simple, online process. If you add
one constraint, the system immediately applies the constraint to all subsequent
transactions. The constraint creation process also checks the existing table to
ensure that all existing rows conform to the new constraint.
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When SQL verifies the constraints on the input data, the potential message
traffic between servers and requesters might be increased when error
messages are generated on invalid data.
Evaluate your application to determine the best use of data checking: constraints
versus program code. For more information, see Creating Constraints on Data on
page 5-51.
Creating Logical Views of Data
Logical views of the database are groupings of data different from the physical
database. SQL/MP is efficient for presenting data in logical views; that is, joining tables
or other views to create a new window into the data. These logical views can specify
only those columns or rows of data that meet the given criteria. SQL/MP returns only
the subset of data, if any, that meets the criteria, thereby reducing message data
transfer between the disk process and your program.
You can predefine and name logical views with the CREATE VIEW statement, or you
can create views logically with a SELECT statement. The performance of these two
methods to obtain the same data is equivalent.
For more information, see Creating Views of Base Tables on page 5-38.
Specifying Block Sizes for Files
To achieve maximum performance for sequential or batch operations, use the largest
block size for the files underlying your tables. The largest block size, 4096 bytes, is the
default size for table and index creation.
There is a locking trade-off, however, when sequential or batch operations run at the
same time as online operations. In this case, use a smaller block size to improve OLTP
performance.
Specific information on file blocks and computing records contained within those blocks
is described under Determining the Number of Records per Block on page 5-15.