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SAS Companion for the OpenVMS Environment

Using the V7 Engine

The section describes how to access Version 7 data libraries using the default engine, V7. The V7 engine supports indexing and compression of observations.

When to Use the V7 Engine

Generally, SAS automatically determines the appropriate engine to use for accessing the files in the library. If you want to create a new library with an engine other than the default engine, you can override the automatic selection.

You use the V7 engine to create SAS data libraries on disk and to read from, write to, or update those libraries. The V7 engine is the default engine for new SAS Version 7 data libraries, unless the default engine has been changed with the ENGINE= system option.

How to Select the V7 Engine

There are three ways to select the V7 engine:

Specify V7 as the value of the engine argument in the LIBNAME statement or LIBNAME function, or specify V6TAPE in the Engine: field of the New Library dialog box. You can open the New Library dialog box by issuing the LIBASSIGN command in the command window.
Note: Use BASE as the engine name if you write programs that create new SAS data libraries and you want to create the data libraries in the latest available format. In Version 7, BASE is an alias for the V7 engine, and it will be an alias for newer engines in subsequent releases.
For an existing SAS data library on disk that contains only Version 7 SAS data sets, do not specify a value for engine in the LIBNAME statement or LIBNAME function, or select Default as the type in the Engine: field of the New Library dialog box. The SAS System then selects the V7 engine automatically. SAS also selects the V7 engine automatically if you use the DCL DEFINE command to assign an OpenVMS logical name to an existing Version 7 SAS data library on disk and then use that logical name as a libref in a SAS file specification.
Set the value of the ENGINE= system option to V7. This option tells SAS which engine to use as the default when no engine is specified and there are no existing data sets, or when the directory is in mixed mode.

Member Types Supported

The V7 engine supports files with all Version 7 member types:

ACCESS ITEMSTOR

AUDIT MDDB

BACKUP PROGRAM

CATALOG PUTILITY

DATA SASODS

DMDB UTILITY

FDB VIEW

INDEX

Engine/Host Options for the V7 Engine

The V7 engine provides several engine/host options that control the creating and access of SAS data sets. Most of the following options correspond to options that are available through OpenVMS Record Management Services (RMS).

You can use the following engine/host options with the V7 engine:

specifies the number of OpenVMS disk blocks to allocate initially to a data set when it is created. The value can range from 0 to 2,147,483,647. If the value is 0, the minimum number of blocks that is required for a sequential file is used. OpenVMS RMS always rounds the value up to the next disk cluster boundary.

The ALQ= option (allocation quantity) corresponds to the FAB$L_ALQ field in OpenVMS RMS. For additional details, see the data set option ALQ= and Guide to OpenVMS File Applications.

specifies the number of pages that are preallocated to a file when it is created. The value can range from 1 to 128. The default value is 10. The ALQMULT= option is related to the ALQ= option.

For additional details, see the data set option ALQMULT=.

specifies the size of the internal I/O buffer used for output data sets. The value can range from 0 to the maximum allowed under OpenVMS. The engine tries to use a value in the range of 8,192 to 32,768 if possible. The BUFSIZE= option must be specified in increments of 512.

For additional details, see the data set option BUFSIZE=.

specifies the number of I/O data caches used per SAS file. The value can range from 1 to 16. The default value is 5. The CACHENUM= option is used in conjunction with the CACHESIZ= option.

For additional details, see the data set option CACHENUM=.

controls the size (in bytes) of the data cache used to buffer I/O pages. The value can range from 0 to 65,024. By default, the chosen value is an even multiple of the file's page size. A value of 0 specifies to use no data cache. Memory is consumed for the data cache, and multiple caches may be used for each data set opened. The disadvantage of large CACHESIZ= values is large consumption of memory. The advantage of large CACHESIZ= values is a reduction in the number of I/Os required to read from or write to a file.

The CACHESIZ= and BUFSIZE= options are similar, but they have important differences. The BUFSIZE= option specifies the file's page size, which is permanent. It can only be set on file creation. The CACHESIZ= option is the size of the internal memory cache used for the life of the current open, so it can change any time the file is opened. Also, BUFSIZE= cannot be used as an engine/host option; it is only valid as a data set option.

For additional details, see the data set option CACHESIZ=.

specifies the level of shared access allowed to SAS data sets. Users can be given both read and write access to a data set that is opened for input only. By default, only shared read access is allowed.

For additional details, see the data set option CNTLLEV=.

specifies the number of OpenVMS disk blocks to add each time OpenVMS RMS automatically extends a data set during a write operation. The value can range from 0 to 65,535. OpenVMS RMS always rounds the value up to the next disk cluster boundary. A large value can result in fewer file extensions over the life of the file; a small value results in numerous file extensions over the life of the file. A file with numerous file extensions that may be noncontiguous slows record access.

If the value specified is 0, OpenVMS RMS uses the default value for the process.

The DEQ= option (default file extension quantity) corresponds to the FAB$W_DEQ field in OpenVMS RMS. For additional details, see the data set option DEQ= and Guide to OpenVMS File Applications.

specifies the number of pages to extend a SAS file. The value can range from 1 to 128. The default value is 5.

For additional details, see the data set option DEQMULT=.

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Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.