It is not duplicating physical file data, rather its duplicating at least
the key data which you've built the logical with, and some pointers to
physical file data. Consider what you're asking though. Its similar to
saying, you have a lot of data on your system, and asking if that impacts
performance. You'd have to take into account what activity is going on to
determine the source of the issue. I'm a bit of a novice on system
performance, but I usually start with WRKDSKSTS and refresh a couple times
to see if it looks like disks are busy. Then I do WRKSYSACT and sort by
I/O activity to see what is doing lots of I/O.
If you just implemented some system, one other thing to keep in mind, is
that there are settings that defer logical file maintenance until the file
is used. Maybe you're seeing logicals being organized during the read,
instead of the write, and that's surprising you? I don't know. I've
pasted the CHGLF parameter that controls maintenance.
Access path maintenance . . . . MAINT *SAME, *IMMED, *REBLD,
*DLY
From: Kok.Gregory@xxxxxxxxxxxxxx
To: midrange-l@xxxxxxxxxxxx
Date: 05/20/2016 08:05 AM
Subject: Logical Files (Views) - Impact on Performance (I/O)
Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>
Hello Midrangers.
We recently implemented a new system on our IBM i720 (v6r1m0). Performance
is since negatively impacted and the bottle-neck is massively I/O related.
Disks are not keeping up.
Looking at the size of the systems database, it is 53% Logical Files
(Views).
All these views (LF's) were created (CRTLF) with the attribute FILETYPE =
DATA. (Most LF's reference a single Physical File only, not multiple PF's)
These LF's are occupying physical space on disk (53%... more than half the
actual database) and I'm concerned there is an I/O impact because of this
?
Can someone elaborate on what the FILETYPE = DATA setting does ? Is it
duplicating physical file data and possibly the source of severe I/O
activity ? (Whats the difference between data records and source records
?) Is there any best practice / recommendations re the use of LF's ?
CRTLF (Command - Create Logical File)
Attribute : File type (FILETYPE)
Specifies whether each member of the logical file being created contains
data records, or contains source records for a program or another file.
*DATA
The logical file contains data records.
*SRC
The logical file contains source records. This value cannot be specified
for join logical files.
Thanks,
G
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