CAS vs SAS

[YHelie1]

Hi,

I'm fully aware of the great benefits of in-memory processing provided with CAS, but what exactly makes the following data steps (first in CAS, then typical SAS 9) such a big difference:

OPTIONS FULLSTIMER;
proc cas;
	data casuser.junk;
		array a [100] a1-a100;
		do i=1 to 5000000;	/*5 million iterations*/
			j = 1 / i;
			k = i / j;
			do m = 1 to 10;
				a[m] = j * k * time();
			end;
			output;
		end;
	run;
run;
quit;

data junk;
	array a [100] a1-a100;
	do i=1 to 5000000;	/*5 million iterations*/
		j = 1 / i;
		k = i / j;
		do m = 1 to 10;
			a[m] = j * k * time();
		end;
		output;
	end;
run;

proc CAS process: Real Time: 8.15 seconds
Standard SAS    : Real Time: 28.48 seconds

???

[PaigeMiller]

---

@YHelie1 wrote:

Hi,

I'm fully aware of the great benefits of in-memory processing provided with CAS, but what exactly makes the following data steps (first in CAS, then typical SAS 9) such a big difference:

---

The in-memory processing makes the difference. There is no disk write step in CAS as there is in SAS. Disk write takes longer than in-memory operations.

[Kurt_Bremser · Accepted solution]

Everything in CAS is multi-CPU capable and can spread the load over the grid. SAS 9.4 uses only one computer, and only some procedures (and not the DATA step, AFAIK) are multithreaded.

[yabwon]

A side note. 

You don't have to put CAS-enabled dataset in proc cas. The data step will run perfectly fine on it's own.

If you look into the log you will see something like:

93     proc cas;
NOTE: PROCEDURE CAS used (Total process time):
      real time           0.00 seconds
      user cpu time       0.00 seconds
      system cpu time     0.00 seconds
      memory              10648.53k
      OS Memory           45696.00k
          
94      data casuser.junk;
95       array a [100] a1-a100;
96       do i=1 to 5000000;  /*5 million iterations*/
97         j = 1 / i;
98         k = i / j;
99         do m = 1 to 10;
100          a[m] = j * k * time();
101        end;
102        output;
103      end;
104     run;
NOTE: Running DATA step in Cloud Analytic Services.
NOTE: The DATA step has no input data set and will run in a single thread.
NOTE: The table junk in caslib CASUSER(********************) has 5000000 observations and 104 variables.
NOTE: DATA statement used (Total process time):
      real time           10.73 seconds
      user cpu time       0.00 seconds
      system cpu time     0.01 seconds
      memory              1258.71k
      OS Memory           36888.00k

which means that proc cas stopped before data step was run. 

A side note to the side note:

When I executed "sas" data step it worked half the time:

82      data work.junk;
83       array a [100] a1-a100;
84       do i=1 to 5000000;  /*5 million iterations*/
85         j = 1 / i;
86         k = i / j;
87         do m = 1 to 10;
88           a[m] = j * k * time();
89         end;
90         output;
91       end;
92      run;
NOTE: The data set WORK.JUNK has 5000000 observations and 104 variables.
NOTE: DATA statement used (Total process time):
      real time           5.09 seconds
      user cpu time       3.21 seconds
      system cpu time     1.89 seconds
      memory              643.78k
      OS Memory           35604.00k

But it used more CPU time.

Bart

[yabwon]

One more side note.  Both data steps, the CAS one and the SPRE one are running in a single thread here so you won't be able to see potential of "parallel" datastep.

Bart

[yabwon]

One more thing. CAS has a lot of cool new features and advantages (e.g. "parallelism") but you have to be also aware that not all things form SAS (e.g. functions) will run in CAS, see: https://blogs.sas.com/content/iml/2020/02/19/sas-functions-not-run-in-cas.html

Bart

[Quentin]

---

@yabwon wrote:

One more thing. CAS has a lot of cool new features and advantages (e.g. "parallelism") but you have to be also aware that not all things form SAS (e.g. functions) will run in CAS, see: https://blogs.sas.com/content/iml/2020/02/19/sas-functions-not-run-in-cas.html

Bart

---

And even more interestingly, things like RETAIN will work in CAS, but they work within a thread, not across threads.  There's good documentation on this, e.g. https://documentation.sas.com/doc/en/pgmsascdc/v_039/casdspgm/p0ujjmynr82tfsn1pyp475bhvaib.htm#n1ais...

And I think ( @yabwon  - I didn't know you had CAS, can you confirm?) that in CAS if you do:

data want;
  set have end=eof;
  if eof;
run;

and if it runs multi-threaded,  want will have as many records as there are threads.  Because each thread will have one record where eof=1.  My mental map is that each thread gets it's own PDV.  I think, haven't tested, as I don't have access to CAS.

[yabwon]

Yes @Quentin , it works as you wrote, and does have multiple observations.

Code:

data casuser.have ;
  set sashelp.cars;
  do i=1 to 100;
    output;
  end;
run;


data casuser.want1;
  set casuser.have end=eof;
  if eof;
  sum+invoice;
  t=_threadid_;
run;

Log:

82     data casuser.have ;
83       set sashelp.cars;
84       do i=1 to 100;
85         output;
86       end;
87     run;
NOTE: There were 428 observations read from the data set SASHELP.CARS.
NOTE: The data set CASUSER.HAVE has 42800 observations and 16 variables.
NOTE: DATA statement used (Total process time):
      real time           0.03 seconds
      user cpu time       0.01 seconds
      system cpu time     0.02 seconds
      memory              1532.90k
      OS Memory           37404.00k

88     
89     
90     data casuser.want1;
91       set casuser.have end=eof;
92       if eof;
93       sum+invoice;
94       t=_threadid_;
95     run;
NOTE: Running DATA step in Cloud Analytic Services.
NOTE: The DATA step will run in multiple threads.
NOTE: There were 42800 observations read from the table HAVE in caslib CASUSER(************************).
NOTE: The table want1 in caslib CASUSER(************************) has 36 observations and 18 variables.
NOTE: DATA statement used (Total process time):
      real time           0.04 seconds
      user cpu time       0.01 seconds
      system cpu time     0.00 seconds
      memory              1328.34k
      OS Memory           37400.00k

Bart