Re: Joins vs. explicitly reading multiple files

I would look at the wider picture, not just at the program you are currently considering.

What effect will this joined logical have on those programs which add-to / update / read the 5 physicals?

The MAINT (immediate, delay, rebuild) parameter may also have an impact.


Regards,
John McKay


----- Original Message ----- From: "sjl" <sjl_abc@xxxxxxxxxxx>
Newsgroups: midrange.rpg400-l
To: <rpg400-l@xxxxxxxxxxxx>
Sent: Thursday, September 18, 2008 1:25 PM
Subject: Re: Joins vs. explicitly reading multiple files

James wrote:
Consider 2 scenarios (both using native Record Level Access):
Scenario A: We read from a join-logical with 5 different based-on
physicals
Scenario B: We read from the 5 based-on physicals individually, either
directly or using simple logicals.

In terms of performance, is there any reason to prefer one over the other?


James -

IMO, It really depends on what data you are needing at any given point in
the program. If there is complex logic in the program based on data
retrieved from one of the files (like a master record) and all you need is
data from one of the 5 files to make that decision before drilling deeper,
an I/O to just the record that you need is less expensive in terms of
resource usage if there is logic that would bypass the retrieval of any of
the other 4 records.

One the other hand, using the joined logical file would probably make the
program easier to maintain, so unless 1) you're processing millions of
records or 2) you need to update a record, I would probably use the joined
logical.

Regards,
sjl



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