|SAS/ACCESS Interface to ADABAS Software
creating and using view descriptors, follow these guidelines
to minimize ADABAS processing and your
operating system resources and to reduce the time ADABAS takes
to access data.
- Specify selection criteria to subset the number
of logical records ADABAS returns to
the SAS System.
- Write selection criteria that allow ADABAS to
use inverted lists when possible. This applies whether you specify the selection
criteria as part of the view descriptor or in a SAS program. This is especially
important when accessing a large ADABAS file.
When ADABAS cannot
use an inverted list, it sequentially scans the entire file. You cannot guarantee
that ADABAS will use an inverted list
to process a condition on a descriptor data field, but you can write selection
criteria that allow ADABAS to use available
inverted lists effectively.
- Select only the data fields your program needs.
Selecting unnecessary data fields adds extra processing time and requires
Use a BY statement to specify the order in which logical records
are presented to the SAS System only if the SAS System needs the data in a
particular order for subsequent processing. You can use ADABAS descriptor
data fields only.
As an alternative to using a BY statement, which consumes
CPU time each time you access the ADABAS file,
you could use the SORT procedure with the OUT= option to create a sorted SAS
data file. In this case, the SAS System, not ADABAS,
does the sorting. This is a better approach for data that you want to use
- If a view descriptor describes a large amount
of ADABAS data and you will use the
view descriptor often, it might be more efficient to extract the data and
place them in a SAS data file. See Performance Considerations for more information on when it is best
to extract data.
If you don't need all occurrences of multiple-value fields,
limit the number of occurrences with the MVF statement.
- If you reference data fields in selection criteria
that are not ADABAS descriptors, it
is generally more efficient to put those conditions in a SAS WHERE clause,
not in the view descriptor WHERE clause.
- To optimize WHERE clause processing, the ADABAS interface
view engine uses the ADABAS L3 command
when possible. However, a number of restrictions must be satisfied before
the L3 command can be used. For these restrictions, see How the SAS/ACCESS Interface to ADABAS Works.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.