High-performance analytical procedures determine the data access mode individually for each data set that is used in the analysis. When high-performance analytical procedures run in distributed mode, parallel symmetric or parallel asymmetric mode is used whenever possible. There are two reasons why parallel access might not be possible. The first reason is that for a particular data set, the required SAS Embedded Process is not installed on the appliance that houses the data. In such cases, access to those data reverts to through-the-client access, and a note like the following is reported in the SAS log:
NOTE: The data MYLIB.MYDATA are being routed through the client because a
SAS Embedded Process is not running on the associated data server.
The second reason why parallel data access might not be possible for a particular data set is that the required driver software might not be installed on the compute nodes. In this case, the required data feeder that moves the data from the compute nodes to the data source cannot be successfully loaded, and a note like the following is reported in the SAS log:
NOTE: The data MYLIB.MYDATA are being routed through the client because
the ORACLE data feeder could not be loaded on the specified grid host.
For distributed data in SASHDAT format in HDFS or data in a SAS LASR Analytic Server, parallel symmetric access is used when the data nodes and compute nodes are collocated on the same appliance. For data in a LASR Analytic Server that cannot be accessed in parallel symmetric mode, through-the-client mode is used. Through-the-client access is not supported for data in SASHDAT format in HDFS.
For data in Greenplum databases, parallel symmetric access is used if the compute nodes and the data nodes are collocated on the same appliance and you do not specify the NODES=n option in a PERFORMANCE statement. In this case, the number of nodes that are used is determined by the number of nodes across which the data are distributed. If you specify NODES=n, then parallel asymmetric access is used.
For data in Teradata databases, parallel asymmetric mode is used by default. If your data and computation are collocated on the same appliance and you want to use parallel symmetric mode, then you need to specify GRIDMODE=SYM in the PERFORMANCE statement or you need to set the GRIDMODE=’SYM’ environment variable by using an OPTION SET statement.
High-performance analytical procedures produce a "Data Access Information" table that shows you how each data set that is
used in the analysis is accessed. The following statements provide an example in which PROC HPDS2 is used to copy a distributed
data set named Neuralgia (which is stored in SASHDAT format in HDFS) to a SAS data set on the client machine:
libname hdatlib sashdat
host='hpa.sas.com';
hdfs_path="/user/hps";
proc hpds2 data=hdatlib.neuralgia out=neuralgia;
performance host='hpa.sas.com';
data DS2GTF.out;
method run();
set DS2GTF.in;
end;
enddata;
run;
Figure 3.4 shows the output that PROC HPDS2 produces. The "Performance Information" table shows that PROC HPDS2 ran in distributed mode on a 13-node grid. The "Data Access Information" table shows that the input data were accessed in parallel symmetric mode and the output data set was sent to the client, where the V9 (base) engine stored it as a SAS data set in the Work directory.