Re: just checking to see if record exists - SETLL on multi format logical versus individual files

[Gqcy <gmufasa01@xxxxxxxxx>]

Thanks John,
I am also seeing that the order of my primary file effects this
as well.  There is a great difference when I process by item number 
(which is the order of the BOM files I am linking to), versus if
I process by Descending item Cost order, or Type of Item order.  I would 
guess that difference is because of what you described in your 
alternative method.

-gerald




Voris, John wrote:
> What is happening is that the first SETLL against the first format FMT1
> quickly found a record matching the format.
>
> The subsequent SETLL is doing a position-file-cursor on the index of the
> logical,
> But this SETLL is actually doing a READE of the index until it finds a
> format that matches the format that you requested (the format FMT2).  
>
> So even though it is a SETLL, it is reading and reading and reading,
> throwing away the records that do not match the requested format until
> it finds the requested format.  I'll bet if we could see under the
> covers that you are re-reading the records you just read in FMT1.  
>
> An alternative would be to do a READ LOGICAL, and using the RPG buffer
> to test the format name, but obviously the SETLL FMT2 it is slightly
> quicker since it is further down in the database level.  If you choose
> to re-write the program to READ LOGICAL without specifying a format but
> instead taking whatever format is handed to you, you could then do a
> Select to check the FMT just read, and I'll bet that you see that you
> are already positioned to where you need after doing all the reads of
> FMT1 ...... FMT1, FMT1, FMT1, FMT2, FMT2, FMT2, FMT3, FMT3, FMT3, FMT3
> ....
>
> A CPYF *PRINT or DBU may show you the actual sequence of formats.
>
> There are similar performance problems such as this when you use the DDS
> keyword DYNSLT.
>
>
> > We needed to SETLL on each record format, because we needed to check
> different things 
> > between different BOM files if we would find a record.