SAS Companion for the OpenVMS Operating Environment

Using the V6 Engine

This section describes how to access Version 6 data libraries using the V6 engine. These data libraries are disk-format data libraries, probably the most common type of libraries.

When to Use the V6 Engine

You use the V6 engine to create Version 6 SAS data libraries on disk and to read from, write to, or update those libraries. The V6 engine also enables you to index and compress observations. For more information about indexes and compressing observations, see SAS Language Reference: Concepts.

How to Select the V6 Engine

There are three ways to select the V6 engine:

Specify V6 as the value of the engine argument in the LIBNAME statement or LIBNAME function, or specify V6 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.
For existing V6 SAS data libraries on disk that contain only V6 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 examines the data set attributes and selects the V6 engine automatically.
Set the value of the ENGINE= system option to V6. This system option tells SAS which engine to use as the default when either no engine is specified and there are no existing SAS data sets, or when the directory is in mixed mode.

Member Types Supported

The V6 engine supports files with all Version 6 member types:

ACCESS

CATALOG

DATA (with indexing capabilities)

DMDB

FDB

INDEX

MDDB

PROGRAM

VIEW

Engine/Host Options for the V6 Engine

The V6 engine provides several engine/host options that control the creation 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 V6 engine:

ALQ=

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 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.

CACHESIZ=

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=.

DEQ=

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.

Data Set Options Supported by the V6 Engine

The V6 engine recognizes all the data set options that are documented in SAS Language Reference: Dictionary except the FILECLOSE= option. The engine/host options discussed in Engine/Host Options for the V6 Engine can also be used as data set options when you use the V6 engine. For more information about data set options, see Data Set Options.

System Option Values Used by the V6 Engine

The V6 engine uses the values of the BUFNO= and BUFSIZE= system options to determine permanent physical characteristics of output SAS data sets. For details about these system options, see BUFNO= and BUFSIZE=.

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