Re: Logical Files (Views) - Impact on Performance (I/O)

How did you calculate the the LF's were taking 57% of the space?

The only thing that takes up space in a logical is the key storage.

--For a logical, --
Using DSPFD
Index size . . . . . . . . . . . . . . : 1597440
Total of member sizes . . . . . . . . . . : 1597440

Using DSPOBJD
Storage information:
Size . . . . . . . . . . . . . . . . : 1658880
Offline size . . . . . . . . . . . . : 1630208

--For the physical--
Using DSPFD
Total of member sizes . . . . . . . . . . : 28897280
Storage information:
Size . . . . . . . . . . . . . . . . : 28987392
Offline size . . . . . . . . . . . . : 28938240

Additionally, the amount of space used by a LF has absolutely no effect on
Disk I/O...

The only negative effect a LF has on disk I/O is additional overhead when
one of the key field changes. This can be minimized by sharing access
paths. For example lets say you have the following LFs
LF (keys)
LF1 (FLD1)
LF2 (FLD1, FLD2)
LF3 (FLD1, FLD2, FLD3)

If the LFs were created in order, (LF1, LF2, LF3) then they each take up
space and if FLD1 happens to change, each on has to be maintained.

If however they are created LF3, LF2, LF1; then only LF3 takes any real
space and it's the only object that needs maintained when FLD1 changes.

Charles


On Fri, May 20, 2016 at 7:36 AM, <Kok.Gregory@xxxxxxxxxxxxxx> wrote:

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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