RE: Joins vs. explicitly reading multiple files

You are going to have to test it to make a judgment. I don't use join logicals unless there is a very
good reason to do so. I use scenario B, and we have good performance. It is possible that we could
get better performance with scenario A, but I don't have to deal with the complexities of promoting
join logicals to production, and impact analysis is simplified as well. In addition, joins can
perform poorly depending on the specifics of the files being joined.

My suggestion would be to pick a way for your shop standard based on you shops needs, and use that
method unless you can't. Only optimize when performance is poor enough that the cost to optimize is
easily recovered in much better performance. I would suggest that the difference between scenarios A
and B is nanoseconds in most cases.

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of James Lampert
Sent: Wednesday, September 17, 2008 1:16 PM
To: RPG programming on the AS400 / iSeries
Subject: Joins vs. explicitly reading multiple files

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?