The LIBNAME Statement for Relational Databases

DBSLICEPARM= LIBNAME Option

Controls the scope of DBMS threaded reads and the number of threads.

Default value:	THREADED_APPS,2 (DB2 under z/OS, Oracle, Teradata), THREADED_APPS,2 or 3 (DB2 under UNIX and PC Hosts, HP Neoview, Informix, Microsoft SQL Server, ODBC, Sybase, Sybase IQ)
Valid in:	SAS/ACCESS LIBNAME statement (Also available as a SAS configuration option, SAS invocation option, global SAS option, or data set option)
DBMS support:	DB2 under UNIX and PC Hosts, DB2 under z/OS, HP Neoview, Informix, Microsoft SQL Server, ODBC, Oracle, Sybase, Sybase IQ, Teradata

Syntax
Syntax Description
Details
Examples
See Also

Syntax

DBSLICEPARM=NONE | THREADED_APPS | ALL

DBSLICEPARM=( NONE | THREADED_APPS | ALL<max-threads>)

DBSLICEPARM=( NONE | THREADED_APPS | ALL<, max-threads>)

Syntax Description

Two syntax diagrams are shown here in order to highlight the simpler version. In most cases, the simpler version suffices.

NONE

disables DBMS threaded read. SAS reads tables on a single DBMS connection, as it did with SAS 8 and earlier.

THREADED_APPS

makes fully threaded SAS procedures (threaded applications) eligible for threaded reads.

ALL

makes all read-only librefs eligible for threaded reads. This includes SAS threaded applications, as well as the SAS DATA step and numerous SAS procedures.

max-threads

a positive integer value that specifies the number of threads that are used to read the table in parallel. The second parameter of the DBSLICEPARM= LIBNAME option determines the number of threads to read the table in parallel. The number of partitions on the table determine the number of connections made to the Oracle server for retrieving rows from the table. A partition or portion of the data is read on each connection. The combined rows across all partitions are the same regardless of the number of connections. Changes to the number of connections do not change the result set. Increasing the number of connections instead redistributes the same result set across more connections.

If the database table is not partitioned, SAS creates max-threads number of connections with WHERE MOD()... predicates and the same number of threads.

There are diminishing returns when increasing the number of connections. With each additional connection, more burden is placed on the DBMS, and a smaller percentage of time saved on the SAS step. See the DBMS-specific reference section for details about partitioned reads before using this parameter.

Details

You can use DBSLICEPARM= in numerous locations. The usual rules of option precedence apply: A table option has the highest precedence, then a LIBNAME option, and so on. SAS configuration file option has the lowest precedence because DBSLICEPARM= in any of the other locations overrides that configuration setting.

DBSLICEPARM=ALL and DBSLICEPARM=THREADED_APPS make SAS programs eligible for threaded reads. To see whether threaded reads are actually generated, turn on SAS tracing and run a program, as shown in this example:

options sastrace=",,t" sastraceloc=saslog nostsuffix;
proc print data=lib.dbtable(dbsliceparm=(ALL));
   where dbcol>1000;
run;

If you want to directly control the threading behavior, use the DBSLICE= data set option.

DB2 under UNIX and PC Hosts, Informix, Microsoft SQL Server, ODBC, Sybase, Sybase IQ: The default thread number depends on whether an application passes in the number of threads (CPUCOUNT=) and whether the data type of the column that was selected for purposes of data partitioning is binary.

Examples

Here is how to use DBSLICEPARM= in a PC SAS configuration file entry to turn off threaded reads for all SAS users:

-dbsliceparm NONE

This example shows how to use DBSLICEPARM= as a z/OS invocation option to turn on threaded reads for read-only references to DBMS tables throughout a SAS job:

sas o(dbsliceparm=ALL)

In this example, you can use DBSLICEPARM= as a SAS global option, most likely as one of the first statements in your SAS code, to increase maximum threads to three for SAS threaded applications:

option dbsliceparm=(threaded_apps,3);

You can use DBSLICEPARM= as a LIBNAME option to turn on threaded reads for read-only table references that use this particular libref, as shown in this example:

libname dblib oracle user=scott password=tiger dbsliceparm=ALL;

In this example, you can use DBSLICEPARM= as a table level option to turn on threaded reads for this particular table, requesting up to four connections:

proc reg SIMPLE;
   data=dblib.customers (dbsliceparm=(all,4));
   var age weight;
     where years_active>1;
run;