SAS Companion for the OS/390 Environment

Using V8 Engines

A V8 data library is a physical file that is formatted to be compatible with the V8 engine. The V8 engine format enables you to access any of the SAS data sets in the library directly, without searching through other SAS data sets. You can read or write more than one SAS data set in a disk-format data library in a single DATA step. Note that preceding does not apply to SAS HFS data libraries stored in UNIX System Services directories.

When to Use This Engine

You use the V8 engine to create SAS data libraries on disk and to read from, write to, or update those libraries. The V8 engine also enables you to index and compress observations. For more information about indexes, see SAS Language Reference: Dictionary. For more information about compressing observations, see SAS Language Reference: Dictionary and Determine whether you should compress your data.

The V8 engine is the default engine for SAS data libraries, unless the default engine has been changed with the SAS system option ENGINE=. This engine is also the only engine under OS/390 that provides full support for catalogs in SAS Version 8; members of type ACCESS, PROGRAM, and VIEW; and SAS data libraries under UNIX System Services. It also supports multivolume SAS data libraries on disk. For further information on multivolume libraries, see Allocating Multivolume SAS Data Libraries.

Here are some other important characteristics of the V8 engine for direct access bound data libraries:

The V8 engine makes efficient use of DASD space because it uses fixed-length physical blocks and enables you to have more than one SAS file per track.
You can use standard utilities to move or copy a V8 data library between unlike device types. This can be done only if the block size of the library does not change and is less than or equal to the track size of the target device.

Here are additional characteristics of the V8 engine that apply to all library implementations (direct access bound library, HFS library, and hiperspace library):

The V8 engine provides a convenient way for you to reduce the elapsed time for SAS jobs. Setting the BUFNO= system option or data set option to a value greater than 1 causes multiple pages to be transferred during a single DASD I/O operation. This can substantially reduce the elapsed time for SAS jobs. However, multiple pages may not necessarily be transferred when an index is used in a "read" operation.
It exploits memory above the 16-megabyte line. I/O buffers for permanent V8 data libraries are allocated above the 16-megabyte line.
After a V8 data library is opened, it remains open until the LIBREF is cleared, or until you end the SAS session. At step boundaries within a SAS session, SAS ensures data integrity by writing any necessary control information to the data set.

How to Select the V8 Engine

There are four ways to select the V8 engine:

Specify V8 as the value of the engine argument in the LIBNAME statement or LIBNAME function.
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 8, BASE is an alias for V8, and it will be an alias for newer engines in subsequent releases.
For existing V8 direct access bound data libraries, specify no value for engine in the LIBNAME statement or LIBNAME function. SAS then examines the data set attributes and selects the V8 engine automatically. SAS also selects the V8 engine automatically if you omit the LIBNAME statement or function and use a JCL DD statement or a TSO ALLOCATE command to allocate the library.
Set the value of the SAS system option ENGINE= to V8. This option tells SAS which engine to use as the default when you allocate a new physical file without specifying an engine.
Specify V8 in the Engine field in the SAS Explorer New Library dialog box.

DCB Attributes for Direct Access Bound Libraries with the V8 Engine

The physical file label contains DCB information that describes the data set's characteristics. The operating environment writes the DCB information when it creates the library, using either values that are supplied by the user or the values of several SAS system options. Both the SAS System and OS/390 utility programs use this DCB information during processing.

The following sections provide additional information about DCB parameters for the V8 engine. Also see DCB Attribute Options for more information.

External Allocation: V8 Engine

If you use a JCL DD statement or a TSO ALLOCATE command to allocate a new V8 SAS data library, and if you choose to specify DCB attributes, then you must specify the following DCB attributes:

DSORG=PS
RECFM=FS
BLKSIZE=4096 to 32256 in increments of 512 (The default is 6144.)
LRECL=value, where value is the same as the value for BLKSIZE=.

If you do not specify DCB attributes for a new V8 SAS data library, then SAS supplies the above DCB attributes whenever the V8 engine has been either explicitly or implicitly assigned. (See How to Select the V8 Engine and How SAS Assigns an Engine When No Engine Is Specified for details about how engines are assigned.)

When allocating a V8 data library, choose an appropriate block size. Here are some guidelines. (See also the performance information in Optimizing I/O.)

If most members of the library will have large numbers of observations, choose the optimal block size for the device. (For a 3380, this value is 23040. For a 3390, it is 27648. See your IBM documentation for the optimal block sizes of other devices.) The result is the minimum amount of overhead that is required to map and transfer library DASD blocks, because there will be fewer total blocks to handle.
If most members of the library will contain few observations, or if their size and number of observations vary widely, choose a smaller block size such as 6144. This increases the opportunity for apportioning DASD space among library members, and it generally makes better use of DASD space.

If no block size is specified when a SAS data library is physically opened for the first time, SAS uses the value of the BLKSIZE= system option. If that value is 0, then SAS uses the BLKSIZE(device-type)= system option. If the value of BLKSIZE(device-type)= is 0, SAS uses a block size of 6144 by default.

If you specify a block size that is not an integral multiple of 512, then the number is rounded down to an integral multiple of 512.

Internal Allocation: V8 Engine

If you use the LIBNAME statement or LIBNAME function to allocate a new V8 SAS data library, SAS supplies the following DCB attributes for you:

DSORG=PS
RECFM=FS
BLKSIZE=6144
LRECL=6144

You can override the default value of the BLKSIZE= system option by using the BLKSIZE= option in the LIBNAME statement or LIBNAME function.

Note: If the SAS system option BLKALLOC is in effect, then SAS assigns BLKSIZE= and LRECL= values when the SAS data library is allocated. If NOBLKALLOC is in effect, then SAS assigns BLKSIZE= and LRECL= values when the library is first accessed. [cautionend]

Engine/Host Options for the V8 Engine

The engine/host options that you can supply in the LIBNAME statement, LIBNAME function, or SAS Explorer New Library Assignment dialog box correspond to the JCL or TSO parameters that you would specify if you allocated the SAS data library externally. For bound libraries using the V8 engine, you can specify any of the engine/host options shown in Overview of the V8 and V8TAPE Engines. (For more information about these options and their values, see the description of engine/host options under LIBNAME.) Or you can accept the default values that are derived from the corresponding SAS system options, as follows:

If you do not specify a value for DISP=, the default for existing data sets is DISP=(OLD,KEEP,KEEP). For new data sets, the default depends on how you are allocating the library:
- If you are allocating the library with a LIBNAME statement, LIBNAME function, or with a TSO ALLOCATE command, disposition defaults to DISP=(NEW,CATLG,DELETE).
- If you are allocating the library with a JCL DD statement, disposition defaults to DISP=(NEW,DELETE,DELETE).
- For HFS libraries, the DISP= option is ignored.
In an interactive environment, if you use a LIBNAME statement, LIBNAME function, or the SAS Explorer New Library Assignment dialog box to allocate a data library that does not exist and you do not specify a value for DISP=, one of the following actions occurs:
- If the SAS system option FILEPROMPT is in effect (the default), then a requestor window asks whether you want to create the physical file. If you reply Yes, you are asked whether you want to catalog the data set when it is deallocated, or to delete it.
  For HFS libraries, a requestor window asks whether you want to create the file, but you do not get a second requestor window.
- If the SAS system option NOFILEPROMPT is in effect, an error message is written to the SAS log.
If you do not specify values for the SPACE= parameters, SAS uses the current values of the SAS system options FILEUNIT=, FILESPPRI=, and FILESPSEC=. The defaults are SPACE=(CYL,(1,1)).
If you do not specify a value for VOLSER=, SAS uses the current value of the SAS system option FILEVOL=, if a value for FILEVOL= has been specified at your site.
If you do not specify a value for UNIT=, SAS uses the current value of the SAS system option FILEDEV=. The default is SYSDA.

Note: The default values shown are those that are supplied by SAS. Your SAS system administrator may have changed the default values for your site. [cautionend]

For temporary data libraries, you do not need to specify any options, but you can override any of the default values.

CONTENTS Procedure Output

The PROC CONTENTS output in PROC CONTENTS Output Generated by the V8 Engine shows information that is generated by the V8 engine.

PROC CONTENTS Output Generated by the V8 Engine

The SAS System 1 The CONTENTS Procedure Data Set Name: WORK.ORANGES Observations: 4 Member Type: DATA Variables: 5 Engine: V8 Indexes: 0 Created: 14:27 Tuesday, March 5, 1999 Observation Length: 40 Last Modified: 14:27 Tuesday, March 5, 1999 Deleted Observations: 0 Protection: Compressed: NO Data Set Type: Sorted: NO Label: -----Engine/Host Dependent Information----- Data Set Page Size: 6144 Number of Data Set Pages: 1 First Data Page: 1 Max Obs per Page: 152 Obs in First Data Page: 4 Number of Data Set Repairs: 0 Physical Name: SYS96065.T142625.RA000.USERID.R0000180 Release Created: 7.0000B2 Release Last Modified: 7.0000B2 Created by: USERID Last Modified by: USERID Subextents: 1 Total Blocks Used: 1 -----Alphabetic List of Variables and Attributes----- # Variable Type Len Pos Format Informat Label -------------------------------------------------------------------------------- 2 FLAVOR Num 8 8 4 LOOKS Num 8 24 3 TEXTURE Num 8 16 5 TOTAL Num 8 32 1 VARIETY Char 8 0

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