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ALQ= |
Language element: | data set option |
Default: | enough blocks for 10 data set pages |
Engines: | V6, V7, V8, CONCUR |
Valid as: | data set option, engine or host option |
OpenVMS specifics: | All aspects are host-specific |
Syntax | |
Details | |
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Syntax |
ALQ=allocation-quantity |
Details |
The ALQ= data set option is often used with the BUFSIZE= and DEQ= data set options to control buffer size and disk allocation for more efficient I/O. For example, if an application processes a large SAS data set sequentially, it may be more efficient to use option values like the following:
data mylib.a(bufsize=16384 alq=300 deq=96); . . . more data lines . . . run;
These statements tell SAS to use a buffer size of 16,384 bytes for data set I/O and to allocate 300 disk blocks to the file initially; when more space is needed, it is allocated in 96-block chunks. This potentially reduces the number of file extensions required for the file. Unused disk blocks are deallocated and freed to the file system at close time. This reduces the number of times a file must be extended, potentially creates a more contiguous file, and reduces subsequent access time.
The order of precedence (from highest to lowest) for specifying initial-allocation values and file-extension values is
The ALQ= data set option also corresponds to the FAB$L_ALQ field in the OpenVMS RMS structure. For information about the FAB$L_ALQ field, see Guide to OpenVMS File Applications.
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Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.