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Change is Good

By Steve Hammond

Inside VESOFT covers tips and techniques you can use with VESOFT’s products, especially MPEX.

Everyone relax.

Take a deep breath.

Now exhale.

Okay, repeat after me, “Change is good. Change is good.”

Right, change is good. That’s what they tell us while passing the secretary a note that says, “Hand out the pink skips in 30 minutes.”

But our friends at VEsoft have found a means of making change a bit more palatable in MPEX. Instead of calling it ‘change’ they call it ‘alt’ — sort of like “it’s not a layoff, it’s a repositioning of human assets.”

Enough management bashing, let’s talk about the Phillips head screwdriver in your MPEX toolbox — ALTFILE. Hey, if you can use all of the ALTFILE options with the COPY command, then it must be powerful!

The ALTFILE option that comes in the most handy on my system is CREATOR. Many times (as I have mentioned in earlier columns) I would end up with a file whose creator was not a user in the account. STOREs and RESTOREs would produce errors and as we all know, the inevitable chaos would ensue. But a simple %ALTFILE filename;CREATOR=username restores order, chaos avoided, life continues.

Humor aside, the options available on ALTFILE are important tools for any system manager. If you are getting short on disk space, ALTFILE is there to help (Author’s note: Does anyone get short on disk space these days? I’ve been in the e3000 world for 20 years and I remember the days when ‘disk was expensive.’ But nowadays, disk is so cheap, how can anyone be short on disk?) Options on the ALTFILE command include BLKFACT, SQUEEZE, XLTRIM and FLIMIT. The first of these may be the slickest:

%ALTFILE filename;BLKFACT=...

lets you alter that mystical value - the blocking factor. You can pick your own factor as in: %ALTFILE filename;BLKFACT=128 or you can let it do some arithmetic for you, as in %ALTFILE filename;BLKFACT=256/RECIZE (RECSIZE is the record size of the file). This will give you the highest value of blocking factor such that the resulting factor is less than or equal to 256.

You can let MPEX do a bit of your thinking with %ALTFILE filename;BLKFACT=MIN(1024/RECSIZE,100) which says, give me a blocking factor of the lesser of the two values — 1024 divided by the record size or 100.

But why do all that? How about %ALTFILE filename;

BLKFACT=BEST? This tells MPEX to pick the best blocking factor for your file! Follow that basic rule of data processing — if the computer can do your work for you, let it!

Two ways are available to set the file limit to the end of file — ;SQUEEZE and ;XLTRIM. The latter should be used on MPE/iX so that it saves as much disk space as possible without restricting the growth of the file. A word of warning on setting the file limit to the end of file — I can’t tell you how many times I shot myself in the foot (I currently have a total of three toes) by doing this without thinking about it in advance. Some files need to grow or need just one blank record at the end. Trust me.

But disk space is not the only thing ALTFILE let’s you play with. Forget to LINK or PREP a program with a capability (or worse, something has PM that shouldn’t), you can:

%ALTFILE filename;CAP=+PH (or -PM)

the syntax allows you to do multiples — CAP=+IA,BA,-PM. You can even play with the maximum data and stack values:

%ALTFILE filename;MAXDATA=nnn

%ALTFILE filename;STACK=nnn

How about that file code value — you can change that too! It used to be that some file transfer utilities would not let you set the file code when you moved the file from PC to e3000. MPEX remedied that with:

%ALTFILE filename;CODE=PROG (or NMPRG or even an integer value).

Maybe the one option that gets ignored too often is the DEV= option. This basically lets you move the files from one disc drive to another. Why is that important? Let’s talk simple performance (and trust me I am about to impart to you a majority of everything I know about performance). Imagine your production database has two datasets that get pounded constantly — 10 times as many accesses as the other datasets in the database. You discover that both those datasets are on the same disc drive. As Captain Queeg would have said, “using simple geometric logic,” you realize that a single disc is spinning like a windmill in a tornado. How about moving one of those datasets off that drive and onto another:

%ALTFILE datasetname;dev=other drive number or device class.

You can even manipulate the EOF on a file (and not just reducing it)! The command

%ALTFILE filename;flimit=...

lets you work with the EOF or file limit. You can give it an exact value with:

%ALTFILE filename;flimit=25000

Or you can do some relative computations with:

%ALTFILE filename;flimit=FLIMIT+8000

or

%ALTFILE filename;flimit=EOF*1.5

The last two give you an increase of 8000 on the end of file value and of 50% on that value, respectively.

So we’ve seen that change, or should I say “alt” is good, at least when it comes to MPEX!

Steve Hammond, who works for a trade association in Washington, DC, believes change is good, especially when it comes to underwear.