RE: CHAIN Versus SETLL and READ When Data Needed

["Shannon O'Donnell" <shannon.odonnell@xxxxxxxxxxxxxx>]

Where's the aspirin... 

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Tony Carolla
Sent: Wednesday, February 28, 2007 3:33 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: CHAIN Versus SETLL and READ When Data Needed

1)  Build three LFs keyed identically as the PF, that contain

     A) only the first key field
     B) the first two key fields
     C) the first three key fields

2)  Build a *SRVPGM prototyped as follows (adjust field types as nec):

     d isThere         pr              n
     d   keyfld1                      3a   const
     d   keyfld2                      9p 2 const options(*nopass)
     d   keyfld2                      4p 0 const options(*nopass)

     A)  runs in it's own activation group
     B)  on the first call, opens up a ridiculously overbuffered copy of
the
three files (OVRDBF SEQONLY(*YES 99999) NBRRCDS(99999))
     C)  for each LF, read in key order every record, manually detecting
unique values,
     D)  place them in an allocated chunk of memory, walking the
structure
using ALLOC, BASED, and pointers
     E)  on subsequent lookups, use qsearch to see if the elements exist
     F)  from your app, use the *SRVPGM as follows:

if isThere(key1 : key2 : key3);
   CHAIN (key1 : key2 : key3) fmt;
elseif isThere(key1 : key2);
   CHAIN (key1: key2:) fmt;
elseif isThere(key1);
   CHAIN key1 fmt;
endif;

Items to consider:
     A)  The data in the tables might change throughout the day --
perhaps
the users should notify each other when they make changes, so that they
can
signoff/sign on and rebuild their "arrays"
     B)  The number of unique fields might cause your *SRVPGM to
allocate
too much memory (in each and every client job) -- consider upgrading
your
RAM
     C)  You will have the privelige of being the only one on the planet
who
knows how to make any changes.

PS.  If you do this, you have probably studied one too many "Sorcerer's
Guides"


On 2/28/07, Shannon O'Donnell <shannon.odonnell@xxxxxxxxxxxxxx> wrote:
> I posed this question on MCPressOnline the other day but I would like
to
> get more opinions on it so I'll post it here too.   A shop-standard
> hangs in the balance.
>
>
>
>    Assume that you have an RPG program that has logic such that you
need
> to first see if some data is in a file, based on a key, and then if
so,
> you do something with that data.
>
>
>
>    Further assume that this file has a complex key with three fields.
>
>
>
>     The program logic is such that you check the maximum number of
keys
> for a match down to the minimum number of keys
>
>
>
>      Like this:
>
>
>
>               Key1    Klist
>
>                           Kfld              Fld1
>
>                           Kfld              Fld2
>
>                           Kfld              Fld3
>
>
>
>               Key2     Klist
>
>                           Kfld              Fld1
>
>                           Kfld              Fld2
>
>
>
>               Key3     Klist
>
>                            Kfld             Fld1
>
>
>
>
>
>    Which one of these logic blocks is most efficient?
>
>
>
>    Key1   Setll   file
>
>        If    %FOUND(file)
>
>                Key1   READE file
>
>                        Use Fields
>
>        Else
>
>           Key2    Setll  File
>
>             If   %FOUND(file)
>
>                      Key2 Use Fields
>
>            Else
>
>              Key3  Setll File
>
>                   If   %FOUND(file)
>
>                      Key3 READE file
>
>                Endif
>
>             Endif
>
>           Endif
>
>
>
>
>
>
>
> OR....
>
>
>
>                KEY1  Chain file
>
>                           If       %FOUND(file)
>
>                               Use fields
>
>                          Else
>
>               KEY2   Chain  file
>
>                           If      %FOUND(file)
>
>                               Use Fields
>
>                           Else
>
>               KEY3   Chain file
>
>                           If   %FOUND(file)
>
>                              Use Fields
>
>                          Endif
>
>                          Endif
>
>                          Endif
>
>
>
>
>
> My opinion is that the CHAIN is more efficient from both a
> coding/maintenance standpoint and from an I/O standpoint, but I'm open
> to opinions.
>
>
>
>
>
>
>
>
>
>
>
> --
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