Re: Anyway for RPG Programs to Use Symmetrical Multi Processing? -- MIDRANGE-L

Hi, William:

You can take advantage of SMP and "DB2 Multisystem", if you have asystem with more than one processor activated ... But, to truly takeadvantage of more than one processor requires designing the applicationto use multiple threads. Languages like C and Java support multiplethreads directly. However, it is NOT a trivial exercise to designapplications that can really benefit from the simultaneous execution ofmultiple threads. And, RPGLE and ILE COBOL have somewhat limited supportfor threads, so far.

And, you cannot use multi-threading in any interactive (5250"green-screen") jobs, only in batch.

Now, consider that each OS/400 Batch job IS a separate "task", with one"thread" of execution.

Say you have a batch job that processes a very large database file ortable with millions or billions of records, and it runs for many hours... you could do something like this:

#1. create several different logical files over the base table (PF),where each LF uses select logic to select a subset of the records. Forexample, you might create 10 different LFs where each LF selects 10% ofthe records in the base table.

#2. then, you can submit 10 different copies of your batch job, allrunning the same exact RPG program, but each job does an OVRDBF to use adifferent one of the above LFs, so that each job now works on only a"subset" of the data. (You might want to pass the name of the LF to useas a parameter to the "wrapper" CL for the batch job, so it can dosomething like this in the wrapper CLP:PGM PARM(&FILENAME)

   DCL   VAR(&FILENAME) TYPE(*CHAR) LEN(10)
   ...
   OVRDBF   FILE(thefile) TOFILE(*LIBL/&FILENAME)
   CALL   PGM(yourprogram)
   ...

#3. finally, you may need a "final" job to consolidate the results, forexample, if you are going to produce a report with totals, etc. (Youmight have to modify your program slightly, e.g. to write the results ofeach batch job to a temporary results file, for use by the"finalization" job to total up all of the subtotals, etc.)

The idea here is, if you have multiple processors activated (and on thelarger iSeries and i5 models, such as 550, 570 or 595s, you can have upto 32 or more processors), each job can be running simultaneously on adifferent processor.

Also, even on a single processor machine, when one job is waiting forI/O, one of the other jobs can be running, although I might not create10 LFs in that case, but perhaps only 4, each with 25% of the total # ofrecords. The idea here is, while one job waits for I/O, one of theother jobs can be "processing." (Recall that every AS/400 model, fromthe first generation and smallest models, to the latest and largest,have many IOPs and IOAs installed, and these I/O Processors are reallyseparate processors that "off-load" much of the work of I/O from themain or central processor(s), leaving them free to work on other jobs.So, that is how you can see greatly improved performance by splitting upjobs in this way, even on the smaller models, with only one physicalprocessor.)

The "big idea" here is, this is an easy way to get many of the samebenefits of multiple threads, even in languages that do not directlysupport threads, such as OPM RPG/400 or COBOL/400, or ILE RPGLE orCOBOL, which support a limited version of threads. (And, you don't haveto learn many of the complexities of how to write programs that aremulti-threaded.)

I know of some customers who achieved dramatic results using thesesimple techniques. For example, a batch job that was running overnight,and was beginning to run so long that it was still running the nextmorning, was reduced to running in just one or two hours, using thisapproach.

To give credit where credit is due, I learned this technique from one ofthe "masters," Dick Bains of IBM Rochester, while attending a session hepresented at COMMON in Anaheim in 1993(?) ... ;-)

Hope that helps,

Mark S. Waterbury

> William N. Harrell, Jr. wrote:

With the advent of the new hardware 5 or so years back, SQLs take advantage
of Symmetrical Multi-Processing, as long as the system attributes are set
correctly.

Is there any way to code any RPG programs to take advantage of Symmetrical
Multi Processing?  Or would it just be RPGILE with embedded SQL?

I had some old links to IBM on the subject 5 or so years back but they are
now are broken on the IBM support site.