• Subject: RE: Logicals?
  • From: "Cotes, Steven" <cotess@xxxxxxxxxxx>
  • Date: Mon, 3 Nov 1997 11:51:57 -0800

> ----------
> From:         Buck Calabro[SMTP:mcalabro@commsoft.net]
> Sent:         Monday, November 03, 1997 6:06 AM
> To:   Midrange-L
> Subject:      RE:Logicals?
> 
> >>Good day to all;
> >>I am wondering about using logical files; say I have a logical built
> >>over a large file and we need another logical which is very close to
> the
> >>structure of the already logical file, with the exception of one
> field
> >>and the logicals key sequence.  Is there another way to manipulate
> the
> >>existing logical (without having to build another logical)?
> >>I appreciate all responses
> >>:-Tim & Dana Truax-:
> >
> >
> >So why are you against another logical?  How many do you have over
> the
> >PF?  10?  50?
> >
> >If you need it build it.  Especially if it will be used by users
> using 
> >Query, SQL, etc.   Or use OPNQRYF or something.  How many records?
> 
> Agreed.
> The AS/400 is very very good at amanging access paths; even over large
> 
> files.  My prior employer's standard was to build a logical when
> needed
> for an interactive application, and to use OPNQRYF when needed for
> batch.
> I'm not sure if I'd follow that advice anymore, because the
> performance of
> the machine has become very, very good.
> 
> Also, be aware that if you have multiple logical files with the same
> key
> structure, the /400 will share the access path, minimising the
> overhead
> involved in maintaining the access path...
> 
> Buck Calabro
> Commsoft
> 
        Also agree, except..
        The system can only share paths when the new logicals do not add
fields.
        That means if you have an existing logical L1 that is built over
fields
        A and B. And you create logical L2 built over fields A, B and C,
they
        will not share access paths. To have them share, you need to
delete
        L1, create L2, and then re-create L1.
        Similar restrictions apply to select/omit data and
ascending/descending
        keys.
        All that aside, if you need another path, build it. The burden
of maintaining
        a path versus having it when you need it is usually worth
paying.

        HTH
        -Steve Cotes
        -cotess@data-io.com
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