Re: CHAIN Versus SETLL and READ When Data Needed

["Steve Landess" <sjl_abc@xxxxxxxxxxx>]

Shannon -

SETLL does NOT move any data or clear any buffers - it simply positions the 
file cursor to be ahead of the record containing the key value specified in 
the KLIST.

So, as far as efficiency goes, I'd say that the first example which uses 
SETLL (except using %EQUAL instead of %FOUND) will be much more efficient 
than using the CHAIN operation code, since CHAIN does perform I/O and if a 
record is not found it clears the buffer area.

- sjl

----- Original Message ----- 
From: "Shannon O'Donnell" <shannon.odonnell@xxxxxxxxxxxxxx>
To: "RPG programming on the AS400 / iSeries" <rpg400-l@xxxxxxxxxxxx>
Sent: Wednesday, February 28, 2007 1:27 PM
Subject: CHAIN Versus SETLL and READ When Data Needed


> 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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