Date:         Mon, 12 Feb 2007 09:43:53 -0500
Reply-To:     Michael Raithel <michaelraithel@WESTAT.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Michael Raithel <michaelraithel@WESTAT.COM>
Subject:      Re: Check it out--we're java programmers
In-Reply-To:  <CA8F89971ADA9F47A6C915BA2397844201EA76F1@MAILBE2.westat.com>
Content-Type: text/plain; charset="us-ascii"

Dear SAS-L-ers,

In one of the many replies to this interesting thread, Sig Hermansen
posted:

> Interesting idea ...
> I wish that the developers would avoid playing on old
> misconceptions about compiled vs. interpreted programs: " ...
> runtime speed (compiled Java runs at a significant multiple
> of the speed of interpreted Base SAS(r))..." I can't imagine
> that either compilation or interpretation of SAS programs
> would save substantial amounts of time in any application. No
> harm in illustrating a few examples of how compiling Java
> programs leads to faster execution times, but global claims
> based on flimsy technical support convince no one but the gullible. S
>

Sig, I address the topic of "pre-compiling" SAS DATA Steps in Chapter
10, The Stored Program Facility, of my book, Tuning SAS Applications on
the OS/390 and z/OS Environments, Second Edition.  Though this book is
aimed at SAS on the mainframe, people running SAS on other platforms can
use the Stored Program Facility to pre-compile SAS DATA steps.  Check it
out in the SAS Online Documentation:


http://support.sas.com/onlinedoc/912/getDoc/lrcon.hlp/a000763412.htm

As I note in my book: unlike "traditional" languages that first compile
program code into object modules, and then link edited the object
modules into load modules, SAS:

1. loads SAS system modules into memory
2. compiles the source code into "intermediate code"--not an object
module
3. turns control over to the instructions of the "intermediate code" to
begin program execution

Because SAS programs "compile and go" in a single step, programmers are
not burdened with having to go through the formal compile and link steps
of many other languages.  However, this means that a finished production
program executed 1,000,427 times, must compile 1,000,427 times--a waste
of computer resources if one looks at the big picture.  Consequently,
the SAS Institute developed the Stored Program Facility so that
completed DATA steps could be compiled once and the intermediate code
stored for repeated execution.

There are a couple of issues with the Stored Program Facility that have
relegated it to the bottom of my own personal SAS toolbox.  The first is
that most of the wallclock time for a given DATA Step is consumed in
processing data and doing the actual work specified by the DATA Step;
not in compiling it.  So, I usually do not save very much time by
pre-compiling.  And, it takes time, effort, and planning to pre-compile,
store the program somewhere, modify programs to execute the pre-compiled
DATA step, etc.  All of this effort is usually not worth the savings I
get.

Secondly, you don't really achieve significant run time reductions
unless you have very big DATA Steps.  Pre-compiling smaller ones doesn't
usually save you very much in computer resources.

Without rehashing Chapter 10, the main considerations are:

1. The size of the DATA Steps
2. The number of DATA Steps in a program
3. The frequency of DATA Step execution
4. The volatility of the DATA Step (to being modified).

So, wrapping up this wordy contribution--fellow SAS-L-ers who are really
interested in pre-compilation of SAS code should check out the Stored
Program Facility.  But, don't get your hopes up that it will lead to SAS
Application Performance Nirvana!

All, best of luck with your SAS endeavors!


I hope that this suggestion proves helpful now, and in the future!

Of course, all of these opinions and insights are my own, and do not
reflect those of my organization or my associates. All SAS code and/or
methodologies specified in this posting are for illustrative purposes
only and no warranty is stated or implied as to their accuracy or
applicability. People deciding to use information in this posting do so
at their own risk.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Michael A. Raithel
"The man who wrote the book on performance"
E-mail: MichaelRaithel@westat.com

Author: Tuning SAS Applications in the MVS Environment

Author: Tuning SAS Applications in the OS/390 and z/OS Environments,
Second Edition
http://www.sas.com/apps/pubscat/bookdetails.jsp?catid=1&pc=58172

Author: The Complete Guide to SAS Indexes
http://www.sas.com/apps/pubscat/bookdetails.jsp?catid=1&pc=60409

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
As long as you derive inner help and comfort from anything, keep it. -
Mahatma Gandhi
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